Next week the House of Commons will vote on whether there should be a 'Mansion Tax' - a levy placed on homes worth over £2m designed to bring "fairness" to the tax system. It is a signature Lib Dem policy that the deputy prime minister has thus far been unable to convince George Osborne to include in his Budgets.
Always keen to cause mischief by exposing splits in the coalition, Ed Miliband and Ed Balls decided to borrow the policy and then use an Opposition Day debate in the Commons to put it to a, purely symbolic, vote on Tuesday. The scamps.
Chris Leslie MP, Labour's shadow financial secretary to the Treasury, said the vote was "a chance for the Liberal Democrats to finally vote for something that was in their manifesto".
The full text of the motion is:
“That this House believes that a mansion tax on properties worth over £2million, to fund a tax cut for millions of people on middle and low incomes, should be part of a fair tax system and calls on the Government to bring forward proposals at the earliest opportunity”.
The vote is win-win for Labour. Should the Lib Dems decide to make a stand and support the motion, which after all was their policy in the first place, Miliband can claim to have split the coalition on a hugely symbolic issue.
But if the junior coalition partner decides to stick with the Tories and vote down the motion, it allows Labour to attack them for abandoning their principles.
It is not a problem lost on the Lib Dem leadership. Tim Farron, the party president, said in an interview with The House magazine on Thursday he had yet to make up his mind. "They’ve [Labour] been opportunistic, they’ve been mischievous. That doesn’t mean we shouldn’t consider it as an opportunity," he said.
Business secretary Vince Cable, who has vocally advocated for a Mansion Tax both inside cabinet and in public, has said he would not rule out voting with Labour.
And ahead of the Eastleigh by-election, Nick Clegg said David Cameron was "stuck in the past" in his opposition to a Mansion Tax.
In preparation for the Tuesday's Commons debate Balls will no doubt have a stack of Lib Dem quotes backing the tax piled high on his desk.
Of couse there is another problem for the Lib Dems. If they vote in favour of a symbolic motion calling for a Mansion Tax but fail to secure its actual introduction in the Budget - which Cameron has ruled out - Labour can easily ask what the point is of the Lib Dems being in government.