David Cameron has called on Gordon Brown to investigate claims by ex-transport secretary Stephen Byers that he secured secret deals with ministers on behalf of commercial firms.
Byers was secretly filmed by journalists from Channel 4 and the Sunday Times, who posed as representatives of an American lobbying firm.
He claimed that he successfully lobbied the transport secretary, Lord Adonis, on behalf of National Express over the termination of a rail franchise contract. He also said that he persuaded the business secretary, Lord Mandelson, to tone down rules on food labeling on behalf of Tesco.
Adonis and Mandelson both denied the claims, as did both companies. Byers said that he had greatly exaggerated his influence.
Other former Labour ministers, including Patricia Hewitt and Geoff Hoon, were also filmed offering to use their access and influence in return for money.
The Tories and Lib Dems are referring Byers to the parliamentary commissioner for standards.
Cameron said that this raised wider questions about sleaze rules, and called for Brown to investigate any further possible breaches. He said: "These are shocking allegations. I have been warning for some time that lobbying would be the next scandal to hit politics."
Senior Labour figures condemned the alleged actions of these MPS, and said that a crackdown on lobbying would be included in the party's election manifesto.
Thirteen Labour MPs and seven Tories were approached. The Conservative whips' office was alerted to the investigation after Tory MP Julie Kirkbride became suspicious of a fake lobbyist.
