George Osborne gleefully unveiled analysis on Monday that suggested Labour would spend billions more if it won this year's election.
The Chancellor dismissed accusations from reporters that the "cost analysis of Labour party policy" by Treasury civil servants, working under assumptions about Labour policies made by Tory aides, was just a "load of nonsense".
Labour reacted with fury, saying it was a "dodgy dossier riddled with untruths" about their spending plans.
Shadow chancellor Ed Balls went on: “It isn’t an impartial exercise but a political smear based on false assumptions made by Tory advisers, including dozens of claims which are not even Labour’s policies."
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Senior Conservative MP's Hold A Joint Press Conference(01 of29)
LONDON, ENGLAND - JANUARY 05: L-R Sajid Javid, Secretary of State for Culture, Media and Sport, Secretary of State for Education Nicky Morgan, British Chancellor of the Exchequer George Osborne, Home Secretary Theresa May and Leader of the House of Commons William Hague speak to members of the media during a press conference on January 5, 2015 in London, England. The Conservative party members used the press conference to cast doubt on Labours spending commitments, claiming they cannot be fulfilled without either tax rises or more borrowing. (Photo by Dan Kitwood/Getty Images) (credit:Dan Kitwood via Getty Images)
BRITAIN-POLITICS-VOTE-CONSERVATIVE(02 of29)
British Chancellor of the Exchequer George Osborne (L) and British Home Secretary Theresa May (R) attend a Conservative Party press conference to present a their cost analysis of the opposition Labour party policy in central London on January 5, 2015. Britain goes to the polls in a general election on May 7, 2015. AFP PHOTO / ANDREW COWIE (Photo credit should read ANDREW COWIE/AFP/Getty Images) (credit:ANDREW COWIE via Getty Images)
Conservative press conference(03 of29)
Chancellor George Osborne speaks during the Conservative press conference with Theresa May, Home Secretary, William Hague, First Secretary of State and Leader of the House of Commons, Sajid Javid, Culture Secretary and Nicky Morgan, Education Secretary and Minister for Women and Equalities at Altitude 360, London. (credit:Anthony Devlin/PA Wire)
Senior Conservative MP's Hold A Joint Press Conference(04 of29)
LONDON, ENGLAND - JANUARY 05: Chancellor of the Exchequer George Osborne, speaks to members of the media during a press conference on January 5, 2015 in London, England. The Conservative party members used the press conference to cast doubt on Labours spending commitments, claiming they cannot be fulfilled without either tax rises or more borrowing. (Photo by Dan Kitwood/Getty Images) (credit:Dan Kitwood via Getty Images)
Conservative press conference(05 of29)
Chancellor George Osborne speaks during the Conservative press conference with Theresa May, Home Secretary, William Hague, First Secretary of State and Leader of the House of Commons, Sajid Javid, Culture Secretary and Nicky Morgan, Education Secretary and Minister for Women and Equalities at Altitude 360, London. (credit:Anthony Devlin/PA Wire)
Conservative press conference(06 of29)
Chancellor George Osborne speaks during the Conservative press conference with Theresa May, Home Secretary, William Hague, First Secretary of State and Leader of the House of Commons, Sajid Javid, Culture Secretary and Nicky Morgan, Education Secretary and Minister for Women and Equalities at Altitude 360, London. (credit:Anthony Devlin/PA Wire)
Senior Conservative MP's Hold A Joint Press Conference(07 of29)
LONDON, ENGLAND - JANUARY 05: Chancellor of the Exchequer George Osborne, speaks to members of the media during a press conference on January 5, 2015 in London, England. The Conservative party members used the press conference to cast doubt on Labours spending commitments, claiming they cannot be fulfilled without either tax rises or more borrowing. (Photo by Dan Kitwood/Getty Images) (credit:Dan Kitwood via Getty Images)
Senior Conservative MP's Hold A Joint Press Conference(08 of29)
LONDON, ENGLAND - JANUARY 05: Sajid Javid, Secretary of State for Culture, Media and Sport, Secretary of State for Education Nicky Morgan, British Chancellor of the Exchequer George Osborne, Home Secretary Theresa May and Leader of the House of Commons William Hague on January 5, 2015 in London, England. The Conservative party members used the press conference to cast doubt on Labours spending commitments, claiming they cannot be fulfilled without either tax rises or more borrowing. (Photo by Dan Kitwood/Getty Images) (credit:Dan Kitwood via Getty Images)
BRITAIN-POLITICS-VOTE-CONSERVATIVE(09 of29)
British Chancellor of the Exchequer George Osborne attends a Conservative Party press conference to present their cost analysis of the opposition Labour party policy in central London on January 5, 2015. Britain goes to the polls in a general election on May 7, 2015. AFP PHOTO / ANDREW COWIE (Photo credit should read ANDREW COWIE/AFP/Getty Images) (credit:ANDREW COWIE via Getty Images)
BRITAIN-POLITICS-VOTE-CONSERVATIVE(10 of29)
British Chancellor of the Exchequer George Osborne attends a Conservative Party press conference to present their cost analysis of the opposition Labour party policy in central London on January 5, 2015. Britain goes to the polls in a general election on May 7, 2015. AFP PHOTO / ANDREW COWIE (Photo credit should read ANDREW COWIE/AFP/Getty Images) (credit:ANDREW COWIE via Getty Images)
BRITAIN-POLITICS-VOTE-CONSERVATIVE(11 of29)
British Chancellor of the Exchequer George Osborne attends a Conservative Party press conference to present their cost analysis of the opposition Labour party policy in central London on January 5, 2015. Britain goes to the polls in a general election on May 7, 2015. AFP PHOTO / ANDREW COWIE (Photo credit should read ANDREW COWIE/AFP/Getty Images) (credit:ANDREW COWIE via Getty Images)
BRITAIN-POLITICS-VOTE-CONSERVATIVE(12 of29)
British Chancellor of the Exchequer George Osborne attends a Conservative Party press conference to present a their cost analysis of the opposition Labour party policy in central London on January 5, 2015. Britain goes to the polls in a general election on May 7, 2015. AFP PHOTO / ANDREW COWIE (Photo credit should read ANDREW COWIE/AFP/Getty Images) (credit:ANDREW COWIE via Getty Images)
BRITAIN-POLITICS-VOTE-CONSERVATIVE(13 of29)
British Home Secretary Theresa May attends a Conservative Party press conference to present a their cost analysis of the opposition Labour party policy in central London on January 5, 2015. Britain goes to the polls in a general election on May 7, 2015. AFP PHOTO / ANDREW COWIE (Photo credit should read ANDREW COWIE/AFP/Getty Images) (credit:ANDREW COWIE via Getty Images)
BRITAIN-POLITICS-VOTE-CONSERVATIVE(14 of29)
British Education Secretary Nicky Morgan attends a Conservative Party press conference to present a their cost analysis of the opposition Labour party policy in central London on January 5, 2015. Britain goes to the polls in a general election on May 7, 2015. AFP PHOTO / ANDREW COWIE (Photo credit should read ANDREW COWIE/AFP/Getty Images) (credit:ANDREW COWIE via Getty Images)
Conservative press conference(15 of29)
Chancellor George Osborne (centre) speaks during the Conservative press conference with (from left) Sajid Javid, Culture Secretary, Nicky Morgan, Education Secretary and Minister for Women, Theresa May, Home Secretary, William Hague and First Secretary of State and Leader of the House of Commons, and Equalities at Altitude 360, London. (credit:Anthony Devlin/PA Wire)
Conservative press conference(16 of29)
Chancellor George Osborne (centre) arrives for the Conservative press conference with (from left) Sajid Javid, Culture Secretary, Nicky Morgan, Education Secretary and Minister for Women, Theresa May, Home Secretary, William Hague and First Secretary of State and Leader of the House of Commons, and Equalities at Altitude 360, London. (credit:Anthony Devlin/PA Wire)
Conservative press conference(17 of29)
Chancellor George Osborne speaks during the Conservative press conference with Theresa May, Home Secretary, William Hague, First Secretary of State and Leader of the House of Commons, Sajid Javid, Culture Secretary and Nicky Morgan, Education Secretary and Minister for Women and Equalities at Altitude 360, London. (credit:Anthony Devlin/PA Wire)
Conservative press conference(18 of29)
Chancellor George Osborne (centre) speaks during the Conservative press conference with (from left) Sajid Javid, Culture Secretary, Nicky Morgan, Education Secretary and Minister for Women, Theresa May, Home Secretary, William Hague and First Secretary of State and Leader of the House of Commons, and Equalities at Altitude 360, London. (credit:Anthony Devlin/PA Wire)
Conservative press conference(19 of29)
Karren Brady attends as Chancellor George Osborne speaks during the Conservative press conference with Theresa May, Home Secretary, William Hague, First Secretary of State and Leader of the House of Commons, Sajid Javid, Culture Secretary and Nicky Morgan, Education Secretary and Minister for Women and Equalities at Altitude 360, London. (credit:Anthony Devlin/PA Wire)
Conservative press conference(20 of29)
Chancellor George Osborne (centre) speaks during the Conservative press conference with (from left) Sajid Javid, Culture Secretary, Nicky Morgan, Education Secretary and Minister for Women, Theresa May, Home Secretary, William Hague and First Secretary of State and Leader of the House of Commons, and Equalities at Altitude 360, London. (credit:Anthony Devlin/PA Wire)
BRITAIN-POLITICS-VOTE-CONSERVATIVE(21 of29)
(L-R) British Culture Secretary Sajid Javid, Education Secretary Nicky Morgan, Chancellor of the Exchequer George Osborne, Home Secretary Theresa May and Leader of the British House of Commons William Hague attend a Conservative Party press conference to present a their cost analysis of the opposition Labour party policy in central London on January 5, 2015. Britain goes to the polls in a general election on May 7, 2015. AFP PHOTO / ANDREW COWIE (Photo credit should read ANDREW COWIE/AFP/Getty Images) (credit:ANDREW COWIE via Getty Images)
Conservative press conference(22 of29)
Chancellor George Osborne (centre) arrives for the Conservative press conference with (from left) Sajid Javid, Culture Secretary, Nicky Morgan, Education Secretary and Minister for Women, Theresa May, Home Secretary, William Hague and First Secretary of State and Leader of the House of Commons, and Equalities at Altitude 360, London. (credit:Anthony Devlin/PA Wire)
BRITAIN-POLITICS-VOTE-CONSERVATIVE(23 of29)
British Home Secretary Theresa May attends a Conservative Party press conference to present their cost analysis of the opposition Labour party policy in central London on January 5, 2015. Britain goes to the polls in a general election on May 7, 2015. AFP PHOTO / ANDREW COWIE (Photo credit should read ANDREW COWIE/AFP/Getty Images) (credit:ANDREW COWIE via Getty Images)
Senior Conservative MP's Hold A Joint Press Conference(24 of29)
LONDON, ENGLAND - JANUARY 05: Sajid Javid, Secretary of State for Culture, Media and Sport, Secretary of State for Education Nicky Morgan, British Chancellor of the Exchequer George Osborne, Home Secretary Theresa May and Leader of the House of Commons William Hague on January 5, 2015 in London, England. The Conservative party members used the press conference to cast doubt on Labours spending commitments, claiming they cannot be fulfilled without either tax rises or more borrowing. (Photo by Dan Kitwood/Getty Images) (credit:Dan Kitwood via Getty Images)
Senior Conservative MP's Hold A Joint Press Conference(25 of29)
LONDON, ENGLAND - JANUARY 05: Sajid Javid, Secretary of State for Culture, Media and Sport speaks to members of the media during a press conference on January 5, 2015 in London, England. The Conservative party members used the press conference to cast doubt on Labours spending commitments, claiming they cannot be fulfilled without either tax rises or more borrowing. (Photo by Dan Kitwood/Getty Images) (credit:Dan Kitwood via Getty Images)
BRITAIN-POLITICS-VOTE-CONSERVATIVE(26 of29)
British Culture Secretary Sajid Javid attend a Conservative Party press conference to present a their cost analysis of the opposition Labour party policy in central London on January 5, 2015. Britain goes to the polls in a general election on May 7, 2015. AFP PHOTO / ANDREW COWIE (Photo credit should read ANDREW COWIE/AFP/Getty Images) (credit:ANDREW COWIE via Getty Images)
Senior Conservative MP's Hold A Joint Press Conference(27 of29)
LONDON, ENGLAND - JANUARY 05: Home Secretary Theresa May speaks to members of the media during a press conference on January 5, 2015 in London, England. The Conservative party members used the press conference to cast doubt on Labours spending commitments, claiming they cannot be fulfilled without either tax rises or more borrowing. (Photo by Dan Kitwood/Getty Images) (credit:Dan Kitwood via Getty Images)
Senior Conservative MP's Hold A Joint Press Conference(28 of29)
LONDON, ENGLAND - JANUARY 05: L-R Secretary of State for Education Nicky Morgan, British Chancellor of the Exchequer George Osborne, Home Secretary Theresa May and Leader of the House of Commons William Hague arrive to speak to members of the media during a press conference on January 5, 2015 in London, England. The Conservative party members used the press conference to cast doubt on Labours spending commitments, claiming they cannot be fulfilled without either tax rises or more borrowing. (Photo by Dan Kitwood/Getty Images) (credit:Dan Kitwood via Getty Images)
Conservative press conference(29 of29)
Chancellor George Osborne (centre) speaks during the Conservative press conference with (from left) Sajid Javid, Culture Secretary, Nicky Morgan, Education Secretary and Minister for Women, Theresa May, Home Secretary, William Hague and First Secretary of State and Leader of the House of Commons, and Equalities at Altitude 360, London. (credit:Anthony Devlin/PA Wire)
Osborne would understand his rival's irritation all too well, having lashed out at Labour ministers in 2010 when they produced their own dossier in government just before the general election attacking Tory spending plans.
David Cameron led the Tory response, calling the publication a "dodgy dossier full of lies" and "complete junk". Meanwhile, then shadow chancellor George Osborne said: "The credibility of Labour lies about Conservatives has collapsed."
In eerily similar tones to Balls' complaint, the senior Tory went on: "The dossier includes commitments we have never made, wild exaggerations of our costed policies, and, in some cases, admissions that some changes would actually be cheaper than we have budgeted for."
In fact, Osborne appears to have quite a talent for railing at something in opposition, before doing exactly the same in government.
In January 2010, he tore into the then Labour chancellor Alistair Darling's proposed "Financial Responsibility" bill, which sought to enshrine in law a Labour pledge to halve the deficit in two years. Fast forward nearly five years, and Osborne himself is now keen on pushing his own very similar bill (or "Charter of Budget Responsibility"), despite having once labelled such measures a "con".
You could say, with apologies to George Bush and John Kerry, that Osborne was against dodgy dossiers before he was for them.