Former ministers would be barred for two years from lobbying government for the private sector, under proposals announced by David Cameron yesterday.

The Tory leader said that he would dock the ministerial pensions of those who ignored guidelines for lobbying. He promised to shine “the light of transparency” on lobbying, and portrayed the Tories as willing to transfer power from Westminster to ordinary people. He contrasted his leadership — “a new generation at ease with openness and accountability” — with “this shameless defender of the old elite”, Gordon Brown.

Mr Cameron toned down an attack on the Prime Minister for his handling of the three Labour MPs facing criminal charges over their expenses amid warnings that rhetoric from all sides could prejudice a fair trial. Mr Cameron’s aides had briefed overnight that in his speech he would accuse Mr Brown of tolerating the “disgusting sight of Labour MPs [abusing] parliamentary privilege... to save their skins and avoid prosecution for fraud and wrongdoing”.

Yesterday morning, shortly before he gave his speech, the three — Elliot Morley, MP for Scunthorpe, David Chaytor, MP for Bury North, and Jim Devine, MP for Livingston — were suspended from the party.

They were further cut adrift when the Speaker announced that the trio, who were all barred from standing again, would have their five-figure “golden goodbye” resettlement grants suspended pending the outcome of their trials. And the Labour Party, which uses the solicitors engaged by the MPs, said it would seek legal advice from elsewhere until the case was under way.

In his redrafted speech, Mr Cameron softened his criticism, saying that the recent chapters in the expenses saga were “all too familiar — disappointment, despair, even disgust”.

Tory aides said that the section had been rewritten because Mr Brown had caved in to pressure, rather than for legal reasons. Mr Cameron said that the Prime Minister was in “headlong retreat” over the issue.

Yesterday the Speaker warned MPs to avoid any reference in the House to the case.

On Sunday Alan Johnson, the Home Secretary, had said in a TV interview that people would be aghast if they thought parliamentary privilege gave MPs a “get-out-of-jail card”.

Denis MacShane, the Labour backbencher, said yesterday that the comments by ministers and Mr Cameron, and the withdrawal of the whip, meant that the three had been “effectively declared guilty”. Mr MacShane said: “The newspapers long ago found them guilty. There is no judge or juror who can think otherwise. Any trial would now be a farce as their guilt and punishment... has already been determined.”

Labour further accused the Tories of playing politics over the issue of parliamentary privilege.

Mr Cameron has asked Sir George Young, Shadow Leader of the House, to prepare a Bill to ensure that there could be no doubt that an MP facing criminal charges would stand before a jury. The Liberal Democrats will try today to amend the Constitutional Reform and Governance Bill to do the same thing.

Labour aides said that any legislation would not be retrospective, so would not cover the three MPs and Lord Hanningfield, the Tory peer. Prosecutors believe that a defence of parliamentary privilege will fail.

Mr Cameron used his speech, in Beckton, East London, to depict Labour as being instinctively for centralisation, and his party by contrast as committed to radical political reform: “We are a new generation, come of age in the modern world of openness and accountability, and when we say we will take power from the political elite and give it to the man and woman in the street, it is not just because we believe it will help fix broken politics. It is what we believe, full stop.”

Former ministers are barred for a year from lobbying former colleagues in government. Mr Cameron said he would extend that to two.

• Labour’s election manifesto team is considering plans to give those who inform on benefit cheats a share of any savings to the public purse, it has emerged. Jim Murphy, the Scottish Secretary, has put the idea to Ed Miliband, Labour’s manifesto co-ordinator, and No 10 has also discussed the plan.