Andrew Grice: It's your choice: Dodgy Gordon or Honest David

"My MPs hate me," David Cameron was heard to remark this week. In an attempt to woo – or at least reassure – voters, the Tory leader has alienated his backbenchers by shaming them into paying back more than £250,000 in expenses to authorities in the Commons.

The process has been tough, but a little farcical. Some Tory MPs told the scrutiny panel set up by Mr Cameron they would "take a hit" to make the list of shame long enough – even though they had not exceeded the party's limits for claims under different headings.

Others resisted, fearing bad headlines in their local newspapers, and got away with it.

Mr Cameron struck a conciliatory note when he addressed a hastily-assembled meeting of his MPs on Thursday. The criticism of his actions was less strong than at the MPs' meeting the previous week: this time, there was coded talk about the need to "rebuild relationships". An orchestrated show of support for the leader, led by the rising frontbench star Justine Greening, provoked muttering among the Cameron critics – since as an inner-London MP she does not claim the allowance for a "second home".

The Tory leader told his MPs: "I was elected to lead. That is my responsibility. Collective action [on expenses] is crucial to be taken seriously as a party of government.

"I don't underestimate how difficult it is for you in your constituencies. Paying back money does not equal guilt. To recognise the public's anger, we have to demonstrate some atonement."

He denied using the expenses crisis to purge old guard MPs, saying he would need experienced figures to be ministers if the party wins power. Cameroons hail the parliamentary party's decision to swallow such nasty medicine as a sign it is preparing for the tough decisions of government and leaving behind the luxury of opposition.

The leader's critics tell a different story. "To call it rough justice is the understatement of the century," one told me yesterday.

"There is widespread anger." Another steamed: "We have turned 'innocent until proved guilty' on its head."

There are dark warnings that backbenchers will take their revenge when Prime Minister Cameron needs their support for the tough decisions – not least on public spending cuts – he would seek to push through if the Tories win the election.

"The resentment will last a long time," one former cabinet minister said. "When he looks around for support, he will find it is not there."

We shall see. A first election victory for 18 years would be a great healer. And his Tory critics concede Mr Cameron has outflanked Gordon Brown on expenses, which could have been toxic for the Tories given the revelations about moats, duck islands, swimming pools and servants.

One test for any party leader is whether he can turn setbacks into opportunities. Tony Blair was good at it. Mr Cameron has managed it on MPs' expenses, in which case the price of upsetting his MPs will be worth paying.

Team Cameron hopes it is on the road to turning another negative into a positive. When Andrew Lansley, the shadow Health Secretary, unwisely blabbed on Radio 4 about 10 per cent cuts in other budgets, the Tory machine went into panic mode. But Mr Cameron and George Osborne, while privately livid with Mr Lansley, decided not to treat his remarks as a "gaffe" but to go on the offensive about the need to curb state spending. They have been helped by Mr Brown's stubborn refusal to admit budgets will have to be cut whoever wins the election, an outdated line that I would expect to change soon.

In adversity, the Tories suspect they have stumbled over a core theme – honesty. No, Mr Cameron is not going to repeat Mr Blair's mistake of promising to be "whiter than white," which would only invite ridicule in the current climate. But the Tories may be on to something. In the last two sessions of Prime Minister's Questions, Mr Cameron has chided Mr Brown for not being "straight" with the public about Labour's spending plans. That will ring true with many voters.

So now we know: the Tory riposte to Mr Brown's "investment versus cuts" election choice will be to invite voters to choose between "Honest Dave and Dodgy Gordon".

Perhaps. But there is a serious point here: after the expenses scandal, trust will be a critical election issue. It is not going to be won back overnight, and not even by a change of government. But a party telling it straight – whether by acknowledging the need for spending cuts, or admitting its mistakes on expenses – may win a grudging respect. Time, then, for Mr Brown to tell it straight on public spending when he unveils his "prospectus" for the nation on Monday.