Andrew Grice: This is one policy on which all parties agree

There will never be a good time to reform the outdated way our political parties are funded, since all roads lead to an increase in the amount of money they receive from taxpayers.

Yesterday, the latest attempt to clean up the system by ending big donations was made by the independent Committee on Standards in Public Life. It is a sensible, fair and balanced package – but before the ink was dry the three main parties had distanced themselves from it. Predictably, they agreed an age of austerity is not the right time to increase state funding.

Of course, the public will always oppose such a move. The committee got a different answer in focus groups when it asked the question the other way round: would voters pay 50p a year to prevent donors from buying influence? Nick Clegg will try to make progress on reform without an immediate injection of extra public money. But he will have his work cut out.

All parties talk a good game. But Labour is overly defensive about its links with the unions that provide half its income and the Conservatives like the status quo, with no cap on donations, because they have more big donors. They spent £16.7m on last year's election, compared to Labour's £8m and the Liberal Democrats' £4.8m.

Until the two biggest parties act in the national interest rather than their own self interest, reform will prove elusive.