John Rentoul: If Gordon Brown is wise, he will not be promising to restore trust in government

Restoring the reputation of politics can hardly be done by one who says that is what he is doing

I have a vision of Gordon Brown as he prepares to assume the office of prime minister later this year. Heavily bandaged, one arm in a sling, standing astride a blasted landscape, he says, "Here you are! Don't lose it again," as he holds out a wreath with a label, "Trust in Politics". Like the soldier in Philip Zec's 1945 cartoon, returning "Peace in Europe" to the people, his expression is one of weariness and reproach.

Trying to restore some faith in politics and trust in politicians is the urgent priority of the incoming administration, and has been worrying Brown and his advisers for as long as they have been planning his takeover. Only last weekend, a well-sourced report quoted those close to Brown as saying his government would be "humbler" and "more austere" than Blair's. This is dangerous and unhelpful talk, but we will come to that in a moment.

The vision of Brown inheriting a wasteland is not, of course, one that is complimentary to Tony Blair. I defend most of the outgoing Prime Minister's record, including his decision to join the invasion of Iraq, which is so often blamed for undermining trust in politics. (A lot of people say that they do not "trust" Blair because of the war: what they mean is that they disagreed strongly with him. That is the essence of politics, not a loss of trust in politics.) But I do not support his scorched-earth approach to raising money for the Labour Party, which really has damaged people's respect for politicians, and justifiably so.

Gordon Brown takes over a bombed-out, barren patch of churned mud and a huge financial deficit. Blair quite recklessly threw everything into his personal war effort, namely the battle to match the big guns of Conservative spending at the last election, in order to secure his third term.

The device he used - secret loans totalling £14m from 12 rich men - ran an extraordinary risk. Not only did it burden the party with debt, it was also a Faustian gamble. He was so focused on winning the election that he seems not to have cared what happened afterwards. It was a case of après moi, pas mon problème. Except that it was his problem. Sorting out the party's finances would fall to someone else - Brown, as it turns out - but the reputational damage was largely inflicted on himself. For a leader allegedly so fixated on his legacy and how posterity would judge him, the risk he took was inexplicable.

Now it has all gone wrong, and, because of the extraordinary decision by Sir Ian Blair, the Metropolitan Police Commissioner, to launch a criminal investigation, far worse than anyone could have expected. The Prime Minister has damaged his reputation needlessly (and those of the lenders, who I would describe as moderately to highly blameless). And he leaves Brown beginning his prime ministership bound and bandaged.

The least important legacy is the gaping hole of Labour's £23m debt; more important is the lack of any visible means by which to fill it. Since the cash-for-peerages affair, fewer rich people want to donate to parties. Even if they did, another consequence of the scandal is that Tony Blair was forced to appoint Sir Hayden Phillips to review the rules on party funding, and he has gone for the easy option of a limit on donations.

He also wants to treat the 4 million trade union members who have not opted out of making a small contribution to Labour as individual party donors. He proposes that they should be required to opt in every year, rather than allowed to opt out at any time. It is hard for Labour to defend what would in the private sector be called inertia selling, so a tourniquet is likely to be applied to that source of cash flow.

The most important of Blair's negative legacies, however, is to have lent credence to the easy cynicism of "they're all the same". He was not the same as what went before, even in the matter of party funding. Under the Conservatives no one knew where the money came from. But he was not different enough.

He - and Gordon Brown - made much in their early years of the dream of Labour as a "mass party", converting those 4 million trade unionists into full members of a party that was embedded in local communities. It was always for the birds, as anything with the word community in it usually is. Political parties in most rich democracies had ceased to be social movements long before Blair became Labour leader.

What is slightly surprising about the Labour membership figures slipped out in embarrassment before Christmas is that - at just less than 200,000 - they were so high. You might have thought that Labour really was the hollowed out shell it is often said to be. You might have thought that a social group so allergic to the compromises of power might have made its excuses and left in rather larger numbers by now. After all, Blair inherited only 254,000 members from John Smith, who scored pretty highly on trustworthiness and who enjoyed the double luxury of being in opposition with a reasonable prospect of power.

That ought to put the angst about trust in politics into perspective. There never has been much. That is why the vision of Brown as the bloodied hero seeking to restore the reputation of politics generally is so dangerous to him. It cannot be done easily, if at all, and politics is such a low-trust business at the best of times that it can hardly be done by someone who says that that is what they are doing.

The danger is that either promises will be distrusted or that expectations will be raised only to be dashed (again). Brown's government may be a little different in tone from Blair's - but not that much - and it will still be engaged, after all, in politics.

The best that Brown can do is avoid secret financial arrangements that cast doubt on his motives. If he manages that, what limited trust there was in politics might repair itself a little after a while.

Trust is a matter of reputation built up over time. That means that Brown has the priceless advantage of being one of the few British politicians in a top job for 10 years who has not made a mess of things. But he will not be able to keep that up as Prime Minister - our political and media system is simply too corrosive. His reputation will start to decay the moment he takes over. It would be madness for him to waste any of his valuable reputation in a doomed attempt to "restore" trust in politics, an aim that is almost by definition undeliverable.

The writer is a biographer of Tony Blair and chief political commentator for The Independent on Sunday

j.rentoul@independent.co.uk