Andrew Grice: This could be a Lib Dem bonanza

When the dust eventually settles on the MPs' expenses scandal, who will be the biggest losers, and can there be any winners? In the short term, I suspect that both Labour and the Conservatives will suffer. You would expect the governing party to bleed most after such a shock to the system and this is the biggest one I have seen in 25 years in the Westminster village.

When a party has been in power for 12 years, it is seen as the establishment, and even more in the stocks. It is true that MPs' pay and expenses are decided by MPs in a free vote, not by the Government. But the man in the Dog and Duck will expect the Government to sweep the stables clean of manure (taxpayer-funded, of course).

Gordon Brown tried to show leadership this week. But he was playing catch-up because David Cameron was so quick out of the traps. He named and shamed his own Shadow Cabinet, forcing several members to repay some of their expenses. He threatened to discipline the Old Tories who had used their allowances to maintain their country houses, swimming-pools and moats.

At a hastily called press conference, Mr Cameron looked the real prime ministerial deal. He reminded me of Tony Blair at his best, sniffing the public mood quickly and responding decisively. He also defined himself against his own party's old guard to show that its leadership had changed, as Mr Blair did repeatedly. Mr Cameron even penned a piece in The Sun, as Mr Blair did so often that it looked as if he was on the payroll.

To his credit, Mr Cameron "outed" his right-hand man, Andrew MacKay, who resigned for "double claiming" second-homes allowances with his MP wife. Mr MacKay was not going to be exposed by The Daily Telegraph, which planned to publish a much more innocuous story about him. Mr Cameron also put the MacKay affair into the public domain immediately, even though this diverted media attention from Elliot Morley, the former Labour minister who claimed for a mortgage he no longer had.

In contrast, Labour's handling of the Morley case looks leaden-footed. We are told that Nick Brown, the chief whip, knew of a problem "a week or so" before the Telegraph broke the story, but that he and the Prime Minister did not know the full facts until the eve of publication. So either the Labour high command knew there was trouble ahead and did nothing to pre-empt it, or hoped the Telegraph would not work out the real story, which it did. It would have been more honest – and helped Labour – to announce that Mr Morley had paid back £16,000 two weeks ago. Mr Brown would not have had to announce Mr Morley's suspension as he launched Labour's election campaign. Lesson: openness can be good politics.

Mr Cameron was tested in a crisis and passed. Despite that, I suspect the expenses controversy will harm the Tories too. It doesn't work when Labour attacks "Tory toffs". But it does damage the Tories when the voters see those photographs of Mr Cameron and George Osborne in their Oxford University days. So I suspect this week's pictures of the manor houses and moats will drag the Tories down a bit in the opinion polls. Bad timing in a recession and all the more need for Mr Cameron to convince people that, despite his privileged background, he is New Tory, not Old Tory.

My hunch is that the Tories will do less well in the 4 June European Parliament elections as a result of the expenses furore. The UK Independence Party is a well-placed receptacle for a protest vote against the system. The only comfort for Mr Cameron is that most of the defectors will probably come home to his party at the general election.

Ukip could even push Labour into a humiliating fourth place in the Euro elections, a meltdown by anyone's standards. Strange as it sounds, such a disaster might not trigger a Labour coup against Mr Brown. If it had happened without the expenses row, it would have been blamed on the Prime Minister. But his own party might now judge that it would be unfair for him to take the rap for a pre-election storm that had been brewing for 30 years, as expenses went up because MPs' pay was held down.

My hunch is that this crisis for politics might be good news for the Liberal Democrats. Many people don't see them as part of the now-discredited system. They are good at attracting protest votes. The Telegraph's revelations about their MPs were small beer. They voted for openness over expenses last year when Labour and Tory MPs blocked it.

In Nick Clegg, they have a leader who "gets" the public anger. He recognises that pay and expenses must be taken out of MPs' hands and wants all parties to sign up in advance to whatever is proposed by the inquiry by the Committee on Standards in Public Life. Mr Brown and Mr Cameron won't do that.

Might the Liberal Democrats answer the voters' call for a new politics? Here is a big opportunity for Mr Clegg. And a big test.