When the Lib Dems' plan to raise the income tax threshold to £10,000 by 2015 was discussed in the televised leaders' debates, David Cameron told Nick Clegg: "I would love to take everyone out of their first £10,000 of income tax, Nick...We cannot afford it." The PM has rather changed his tune since then. He now leads a government that will meet that pledge in April 2014, a year earlier than promised, and a party that lists its greatest achievement as "a tax cut for 24 million hardworking people".

With the £10,000 threshold due to take effect when the new tax year begins, there is room for the coalition to go further in the two Budgets that remain before May 2015. Today, in an attempt to reclaim ownership of the policy, Clegg has called on George Osborne to deliver a pre-election tax cut by increasing the allowance to £10,500 and delivering a "workers' bonus" (note the smart framing).

Interviewed on The Andrew Marr Show this morning, he boasted that his plan would mean "an extra £100 in everybody's pocket". Except, of course, it wouldn't. Raising the personal allowance will do nothing for the lowest-paid five million workers, all of whom earn less than £10,000, or the unemployed, the disabled and the retired. As the IFS has shown, those in the second-richest decile gain the most in cash terms from the policy (mainly due to the greater number of dual-earning households), followed by the richest tenth, who gain marginally less due to the gradual removal of the personal allowance after £100,000 (a brilliant piece of stealth redistribution by Alistair Darling). As a percentage of income, it is middle-earners who gain the most, with those at the bottom gaining the least.

Marr failed to challenge Clegg on this point, but Labour and other parties should. Progressive alternatives to raising the income tax threshold include increasing the National Insurance threshold, which currently stands at £7,748, or cutting VAT, which stands at a record 20 per cent and hits the poorest hardest. These policies might not be as politically attractive as a cut in income tax, but they will do more to get money where it is most needed.