Ed Miliband’s dramatic decision to outflank David Cameron on the economy by calling for the 10p rate of income tax to be brought back had been dismissed as a "PR wheeze" by the Conservative MP who has campaigned in favour of the move.
On Thursday the Labour leader said reintroducing the band - controversially scrapped by Gordon Brown - would make society fairer. In a keynote speech, he said the move could be funded by a new "mansion tax" on homes worth more than £2m.
Tory backbenchers, led by Harlow MP Robert Halfon, have been campaigning for the 10p rate to be brought back by George Osborne in next month's Budget.
But writing on The Huffington Post UK, Halfon said Miliband’s surprise announcement was "a half-hearted Damascus conversion" to the cause, suggesting it was made with one eye on the impending Eastleigh by-election.
"Only in 2008, HuffPost readers will remember, the Labour Leader said that abolishing the 10p rate of income tax for the poorest Brits was ‘fairer’, and he voted that way in Parliament," Halfon said.
"What are voters to make of this? In my view, what the public want to know is this: is this just jam for the Eastleigh by-election or is this a substantive policy pledge?
Robert Halfon: Can We Trust Labour's Surprise 10p Announcement?
"Consider the record of the two main parties: Ed Miliband has whipped his MPs to vote against every single tax-cut for the poorest Brits that the Coalition has delivered; whether this is on council tax, fuel duty, or income tax.
"By contrast, Conservatives in government this April will cut income taxes for 25 million people. Two million will have been taken out of income tax altogether.
"And, the poorest who benefited from the 10p rate under Labour (until they scrapped it in 2008) now pay no income tax at all."
Halfon adds: "Today could have been a real policy announcement from Labour, rather than a PR wheeze written on the back of an envelope. As it stands, Labour’s suggestion would only mean an extra £34 a year for a family."
Labour's tax plan has been dismissed by David Cameron, who said it appeared as though it was not properly "costed".
"We'll discover over the course of the day all sorts of problems and issues with a policy that looks like it's been cobbled together overnight," he said.
Lib Dem Chief Secretary to the Treasury Danny Alexander said: "The two Eds are rather late to the party, wanting to cut taxes for those on low and middle incomes.
"After 13 years in government, the only action Ed Balls took was to raise the amount of tax those on low incomes paid by abolishing the 10p rate. It was the biggest tax mistake they ever made and it has taken them until now to realise their error.