Ex-ministers would have to wait two years after leaving office before lobbying a Conservative government, David Cameron said today.
The Tory leader said he wanted to crack down on the "far-too-cosy relationship" between big business and politics.
In a speech at the University of East London, he described the issue of "secret corporate lobbying" as the "next big scandal waiting to happen".
"It's important that businesses, charities and other organisations feel they can make sure their voice is heard - and, indeed, lobbying often makes for better, more workable, legislation," he said.
"But I believe that it is increasingly clear that lobbying in this country is getting out of control."
He said lobbying was now a £2 billion industry and pointed to research from The Hansard Society that estimated some MPs were approached more than 100 times a week by people seeking to influence policy.
"We don't know who is meeting whom. We don't know whether any favours are being exchanged. We don't know which outside interests are wielding unhealthy influence," he said.
"This isn't a minor issue with minor consequences. Commercial interests - not to mention government contracts - worth hundreds of billions of pounds are potentially at stake.
"I believe that secret corporate lobbying, like the expenses scandal, goes to the heart of why people are so fed up with politics."
Mr Cameron said the Conservatives would introduce law changes over the issue.
"Today, the guidelines state that former ministers shouldn't lobby government for at least twelve months after leaving office. We will start by doubling that to two years," he said.
The Ministerial Code would be re-written to ensure anyone who ignores the advice is forced to forfeit "some or all" of their ministerial pension, Mr Cameron added.
"It is the next big scandal waiting to happen," he said.
"It's an issue that crosses party lines and has tainted our politics for too long, an issue that exposes the far-too-cosy relationship between politics, government, business and money."
The Tory leader also used the 30-minute speech to attack the Government over its handling of the expenses scandal.
He said Labour was in a "headlong retreat" over the issue and claimed the decision to discipline the three Labour MPs facing criminal charges represented a "humiliating change" in stance.
"In a humiliating change, they have actually withdrawn the Labour whip from all three of those MPs. They are now in a headlong retreat," said Mr Cameron.
"The last 24 hours, I believe, have shown the instincts of the Conservative Party, when it comes to this issue about expenses, are in tune with the public mood, are in the right place, and Labour's are not."
Mr Cameron said his party had shown "leadership at every stage" over MPs expenses.
He told the audience at the university's Docklands campus that he had asked for a new Parliamentary Privilege Act to be prepared to ensure it was not used by MPs to "evade justice".
His comments come amid claims the trio of Labour MPs facing prosecution over their expenses will argue they are protected by the Act.
In a direct attack on the Prime Minister, Mr Cameron accused Mr Brown of presiding over a regime at Westminster which led to the collapse of public confidence in politics.
"How Gordon Brown can claim to be a reformer with a straight face I just don't know," he said.
"He can't reform the institution because he is the institution: he made it.
"The character of his Government - secretive, power-hoarding, controlling - is his character."
Mr Cameron said the Tories offered the public the chance to elect a "new generation" to help "fix broken politics".
"We are a new generation - come of age in the modern world of openness and accountability," he said.
"When we say we will take power from the political elite and give it to the man and woman in the street, it's not just because we believe it will help to fix broken politics, it's what we believe - full stop."Reuse content