The clip above, recorded during the leaders' debates, shows the Conservative leader attacking the Liberal Democrats' flagship policy of lifting the low-paid out of income tax altogether.
Turning to Clegg, Cameron explains why the Lib Dems' flagship policy is unaffordable: "I would love to take everyone out of their first £10,000 of income tax. ... We cannot afford it."
Five years later and Conservative chancellor George Osborne has confirmed that the personal allowance – the amount of money the government allows you to earn in a year without paying income tax – will hit £11,000. That's up from £6,475 when the coalition came to power.
Osborne, an effective political operator, agreed to the policy when the coalition was formed in 2010. But somewhere along the line he has also managed to completely co-opt it, taking the credit along the way.
This is how Osborne announced the latest increase to the personal allowance in today's budget – emphasising "we" at every opportunity.
We believe that work should pay – and families should keep more of the money they earn. When we came to office, the personal tax-free allowance stood at just £6,500. We set ourselves the goal – even in difficult times – of raising that allowance to £10,000 by the end of the parliament. We have more than delivered on that promise.
In two weeks' time it will reach £10,600.
That's a huge boost to the incomes of working people and one of the reasons we have a record number of people in work. Today I can announce that we go further.
The personal tax-free allowance will rise to £10,800 next year – and then to £11,000 the year after. That's £11,000 you can earn before paying any income tax at all. It means the typical working taxpayer will be over £900 a year better off. It's a tax cut for 27 million people and means we've taken almost 4 million of the lowest paid out of income tax altogether.
It is a coalition policy, so is signed off by the Lib Dems – but Osborne, as chancellor, has the right to announce every increase to the public.
Which means that it's always reported as an Osborne announcement:
The Conservatives can claim credit:
And the Lib Dems are left desperate and shouting, trying to remind people it was their idea all along:
Jim Waterson is a politics editor for BuzzFeed News and is based in London.
Contact Jim Waterson at firstname.lastname@example.org.
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