The move to impose higher taxes on second homes - set out as part of preparations for the 2015 general election manifesto - emerged after Labour pledged to support a mansion tax to fund a return of the 10p starting rate of tax, scrapped by Gordon Brown in 2008.

BBC: Lib Dems look at extending mansion tax

That should not matter to the government, save for one thing: next year, for the first time in a decade, the unions, under a law introduced by Margaret Thatcher, have to ballot their members on whether to maintain a political fund, most of which has traditionally been used to finance the Labour Party.

ECONOMIST: How dangerous is the rise in union militancy?

This was proposed by the Conservatives as part of a scheme to fund the basic pension, but rejected by the Labour Party when it was in opposition.

ECONOMIST: Pensions