George Osborne's deputy Danny Alexander has been accused of using Treasury civil servants as a "coalition propaganda machine" after ordering them to produce a report that was used to attack Labour's spending plans.
Justice secretary Chris Grayling warned that taxpayers would be worse off under Labour, based on the Treasury's analysis which concluded that Labour would borrow £166.2 billion more than the coalition over the next parliament.
Labour's spending plans will cost "£5,500 for every taxpayer in this country", Grayling claimed today.
The Treasury's calculations over the period of 2016/2017 to 2020/2021 forecast Labour would still be borrowing £41 billion in 2019-20 and £32 billion in 2020-21 whereas the coalition is planning to have borrowing down to zero, in analysis that Labour sources said was "based on totally false assumptions about our fiscal commitments".
Dr Nicholas Allen, a senior politics lecturer at Royal Holloway University and expert in political ethics, told the Huffington Post UK that ministers were "playing with fire" as they risked "setting a precedent if they start doing it more than other governments".
He continued: "Government departments have always had to be mindful of opposition spending plans as they have got to put them into effect so in a sense the civil service has to do this kind of analysis in order to be ready should the opposition get into government. However, politicians will inevitably politicize things for partisan advantage."
Teresa Pearce, Labour member of the influential Treasury select committee, branded the report "ridiculous" as the Tories stopped the Office for Budget Responsibility, the government's independent budgetary watchdog from examining Labour's spending plans.
"The Treasury should be spending its time trying to get on top of the Universal Credit project that has been a huge waste of tax-payers money up to now instead of helping the coalition propaganda machine," she told the Huffington Post UK.
"If Grayling really believes what he says then why did the Coalition MPs block the proposal that the OBR should examine both major parties spending plans prior to the general election? They blocked it because it would show that ridiculous claims such this are just plain wrong."
Labour MP Paul Flynn, member of the Public Administration Committee, accused coalition ministers of "politicizing the organs of Government in a pre-election campaign."
"The Public Administration Committee was persuaded to degrade its independent status and indulge in a partisan inquiry into the conduct of civil servants in Scotland," he said. "It is unlikely that they be willing to probe this attempt to distort the role of civil servants in order to discredit the Labour Party."
The report was ordered by Lib Dem chief secretary to the Treasury Danny Alexander in response to a Freedom of Information request from a fellow Lib Dem MP.
A Treasury spokeswoman told the Huffington Post UK: "Successive government administrations have accepted that since government departments provide factual answers to MPs and peers about the costs of identifiable changes in activities or benefits, there is no objection to officials providing Ministers with similarly factual information about clearly identified opposition policies.
"Costings are produced in line with long-established formal guidance set out by the Treasury. The process for this is well established and on the principle that any requests for costings through the Freedom of Information Act should normally result in the costing being published."
Speaking in January, Alexander used the analysis to warn that "Labour have learnt nothing from the past and can't be trusted by the British people on the economy."
At the same time, chancellor George Osborne wrote to his opposite number Ed Balls: "Despite your recent attempts to rebuild a reputation for fiscal responsibility, the truth that was buried in the small print is now clear: the Labour Party is the single biggest risk to the economic recovery."
The Treasury has previously been accused of political bias against after its head, permanent secretary Sir Nicholas Macpherson, published his official advice to the chancellor warning against the dangers of sharing the pound in the event of Scotland gaining independence.