Andrew Grice: Off with their heads! But is Westminster justice fair?

The body count is soaring as party leaders crack down on MPs caught in the expenses mire – but backbenchers are first for the chop

"There's more blood on our carpet than Labour's," one Tory aide reassured me yesterday. It was a revealing comment. Yes, the public does want blood over the expenses scandal. But do they really want the heads of MPs to be chopped off in such an arbitrary way?

MPs complain about "summary justice" as whips are withdrawn and retirements enforced by party leaders – sometimes in frantic phone calls at 10pm when The Daily Telegraph's latest revelations become known.

When the controversy erupted, Gordon Brown and David Cameron competed with each other for the toughest language. Then there was a bizarre race among MPs who had ripped off the taxpayer to pay some of the money back. Now the two parties compete to take the toughest disciplinary action. One Cabinet minister admitted: "Cameron was quick out of the blocks. We have caught up. Now we have got to overtake him."

While both Labour and the Tories have set up disciplinary panels, their leaderships have given themselves a lot of flexibility. So far, it seems that front and backbenchers are being treated differently.

Three old guard Tory backbenchers – Douglas Hogg, Anthony Steen and Sir Peter Viggers – whose gardens were maintained by taxpayers, were shamed into announcing they would stand down at the general election. In contrast, Alan Duncan remains as shadow Commons Leader after admitting he overclaimed for his garden. Bill Wiggin, a Tory whip and contemporary of Mr Cameron at Eton, also got the benefit of the doubt, even though his mistake was similar to the actions of the suspended Labour MPs David Chaytor and Elliot Morley – claiming for a "phantom mortgage."

Some Tories say that removing "bed-blocking" veteran MPs will give an unexpected fillip to the Cameron project to modernise his party.

Labour activists, already seething, wonder why no minister has been referred to the party's panel which can deselect MPs. Backbenchers Mr Chaytor, Mr Morley, Margaret Moran and Ian Gibson will appear before it in the next two weeks but the panel will not consider the cases of Shahid Malik, who stood down as a Justice minister (perhaps temporarily) and the Communities Secretary Hazel Blears, who repaid £13,000 to HM Revenue and Customs after she did not pay capital gains tax on the sale of her London flat.

Desperate to sound tough, Mr Brown said Ms Blears's actions were "totally unacceptable". He hadn't thought it through: if that is the case, why is she still in his Cabinet? And why does he maintain that there is no problem about her Cabinet colleagues James Purnell and Geoff Hoon, who seem to have done something very similar. Another inconsistency.

The two main party leaders, who eventually agreed on interim changes to the expenses system this week, will probably do battle next on what long-term measures are needed. Any crisis – and this is a big one – also brings an opportunity. Supporters of constitutional reform have a spring in their step. They are dusting down their pet schemes and they suddenly make the headlines again. At the cabinet table, young Turks like David Miliband and Mr Purnell urge the Prime Minister to seize the chance to transform our ailing democracy by embracing a "big bang" reform. They want the firework display to include a written constitution, an elected House of Lords, electoral reform for the Commons and a shake-up of party funding.

If it were 1997, it might work. Even in 2007, Mr Brown had a window of opportunity to make a move. He had wooed the reform brigade before taking over from Tony Blair with hints about grand reforms. But his cupboard was pretty bare. His Bill of Rights is stuck in the slow lane, Lords reform and major changes to party funding shelved.

With a general election to be held within a year, unrealistic expectations are being aroused. The older cabinet heads responsible for reform, Jack Straw and Harriet Harman, are drawing up a more limited package that targets the scene of the crime – Parliament. Expect the Government to give up some of its control over the Commons – for example, the power of whips to choose select committee chairs. There will be more time for back-bench legislation and debates. The changes could be tacked on to the Constitutional Renewal Bill already going through Parliament.

Those cabinet ministers who favour state funding of political parties might have a good case in different times. But it would be electoral suicide to propose it now. In any case, it would be difficult to change the funding rules in the run-up to an election and there is little prospect of a sudden consensus on an issue over which the parties have haggled for the past three years.

Indeed, the man in the Dog and Duck, already angry about MPs' expenses, would hardly raise a glass to a government which obsessed about the fine print of constitutional measures in the midst of a recession.

There could be a draft Lords reform Bill – Mr Straw favours an 80 per cent elected second chamber – but there wouldn't be time to push it through before the general election. A written constitution could not be scribbled overnight and the public would have to be consulted. There is a growing consensus among senior Labour figures for the alternative vote – allowing voters to rank candidates in order of preference so the eventual winner enjoys more than 50 per cent support. This would keep the link between an MP and his or her constituency, unlike full-scale proportional representation, but such a momentous change would require validation through a referendum or an election.

Although the reformers should not think a constitutional revolution is imminent, big ideas including electoral and Lords reform may well now feature into the Labour manifesto. It could be a very radical one indeed.

What a shame it will have taken Labour 13 years to get to that point. And that the likely election result means the plans will return to those dusty shelves.

Bill Wiggin

(Conservative, Leominister) Whip, at Eton with David Cameron

Crime: Took £11,000 for mortgage for a property with no mortgage

Punishment: None. Cameron accepts it is an honest mistake as MP could have claimed same for other home

David Chaytor

(Labour, Bury North) Low-key backbencher

Crime: Claimed almost £13,000 for a mortgage he had already repaid

Punishment: Suspended from Parliamentary Labour Party; faces deselection as election candidate

Alan Duncan

(Conservative, Rutland&Melton) shadow Commons leader, responsible for expenses

Crime: Claimed £4,000 for gardening

Punishment: Repays almost £5,000, keeps job in David Cameron's shadow Cabinet

Sir Peter Viggers

(Conservative, Gosport) Backbench grandee

Crime: Claimed more than £30,000 for his garden, including £1,645 for a floating "duck island"

Punishment: ordered by Cameron to stand down at general election

Hazel Blears

(Labour, Salford) Communities Secretary and Blairite cheerleader

Crime: Avoided capital gains tax (CGT) when London flat sold

Punishment: Repaid £13,000 to tax man; Gordon Brown says her actions were "totally unacceptable"

James Purnell and Geoff Hoon

(Labour, Stalybridge & Hyde, Lab Ashfield ) Pensions Secretary, Transport Secretary

Crimes: Did not pay CGT on sale of their London homes

Punishment: None. Gordon Brown says there is "no problem"