Labour has promised a crackdown on lobbying by ex-ministers after several of its senior MPs were filmed apparently offering their services for cash.
The party rushed forward a manifesto pledge for tighter regulation and monitoring as it emerged politicians had claimed to be able to influence policy.
Ex-Cabinet minister Stephen Byers was among retiring MPs interviewed by a fictitious US lobbying firm as part of a secret filming operation for a television documentary. He told an undercover reporter he had secured secret deals with ministers, could get confidential information from Number 10 and was able to help firms involved in price fixing get around the law.
The North Tyneside MP retracted his claims the following day - insisting he had "never lobbied ministers on behalf of commercial interests" and had exaggerated his influence.
The Sunday Times, which carried out the interviews with Channel 4's Dispatches programme, said Mr Byers, who held several key cabinet portfolios such as trade and transport, wanted £5,000 a day.
Another of those filmed was ex-health secretary Patricia Hewitt, who said she "completely rejected" the suggestion that she helped obtain a key seat on a Government advisory group for a client paying her £3,000 a day.
She stressed that the role she had been discussing would only have been taken up after she stepped down as an MP at the imminent election and insisted there was "nothing unusual or improper in the business appointments that I have taken up since leaving Government".
Tory leader David Cameron promised tougher controls last month - warning that secret corporate lobbying was the "next big scandal waiting to happen" in Westminster after expenses.
Stung by the latest revelations - which involved a number of retiring MPs including ex-minister Geoff Hoon and Margaret Moran - Labour said it too would act if it wins the general election.
"There can never be any suggestion that companies and businesses can only speak to government by buying access through MPs or anybody else," a spokesman said. "What this case shows is that we need more transparency in the entire lobbying system. That's why we believe that the time has come to support a Statutory Register of Lobbyists and we will bring forward proposals to that effect in our manifesto, building on the work we have already done to create a voluntary code."