David Cameron calls for 'ex-ministers for hire' probe
David Cameron:"What we need is a government investigation into what these ministers have done"
Conservative leader David Cameron has called for a Commons inquiry into allegations former ministers tried to sell influence for cash.
Labour MPs Stephen Byers, Patricia Hewitt and Geoff Hoon deny breaking any rules after being secretly filmed.
Senior Labour figures condemned their alleged actions and announced a crackdown on lobbying would be included in the party's election manifesto.
Mr Cameron said the "shocking allegations" warranted an inquiry.
The Liberal Democrats said reform of the "whole rotten system" was needed.
Mr Cameron called on Prime Minister Gordon Brown to launch an inquiry into claims about Mr Byers and ministerial meetings - and a separate House of Commons probe into the allegations about the conduct of the MPs.
The Tory leader, who recently said lobbying would be the next big political scandal, said: "I think what it shows is a party that has been in power for far too long and has lost touch with what it's meant to be doing."
The allegations followed a joint Sunday Times and Channel 4 investigation.
The three MPs at the centre of the claims are all ex-ministers who are standing down at next month's election.
Mr Byers was recorded as saying he would work for up to £5,000 a day and was like a "cab for hire".
He told an investigative reporter that he had secured deals with ministers, could get confidential information from No 10 and was able to help firms involved in price-fixing get around the law.
Sitting MPs are not banned from working for corporate clients but the practice is controversial
They must declare any payment in the register of members' interests
Any paid work taken by an ex-minister within two years of leaving office must be cleared by a panel - the Advisory Committee on Business Appointments
They are not allowed to table amendments or vote on bills in exchange for payment
They are normally banned for 12 months from becoming lobbyists in their specialist fields
Labour, the Tories and the Lib Dems all say they want the rules tightened to prevent ex-ministers exploiting their contacts for private gain
After being confronted with the allegations, the MP, who stood down as a minister in 2002, said he had been exaggerating his influence over government policy and had "never lobbied ministers on behalf of commercial interests".
Reports of his claims that he influenced government policy on behalf of National Express and Tesco were firmly rejected by the two companies, which both said they had never employed his services.
The two cabinet ministers Mr Byers is reported as saying he influenced also strongly deny the allegations.
A statement released on behalf of Transport Secretary Lord Adonis said: "There is no truth whatsoever in the suggestion that Stephen Byers came to any arrangement with Andrew Adonis on any matter relating to National Express."
Business Secretary Lord Mandelson said he had "no recollection" of any meeting with Mr Byers about food labelling - the policy area in which he is said to have been interested in.
'Out of touch'
But Lib Dem transport spokesman Norman Baker vowed to report Mr Byers to the Parliamentary Standards Commissioner and said he would ask Parliamentary questions about contacts between Mr Byers and ministers.
Mrs Hewitt, who was also named as part of the investigation, said she "completely rejected" the suggestion she helped obtain a key seat on a government advisory group for a client paying her £3,000 a day.
What on earth did they think they were doing?
Chancellor Alistair Darling
The former health secretary said the role she had been discussing would only have been taken up after she stepped down as an MP at the next election.
The reporters claim former defence secretary Mr Hoon offered to lead delegations to ministers, and said he wanted to make use of his knowledge and contacts in a way that "frankly makes money". He said he charged £3,000 a day.
He said he made clear during an "informal chat" with what he assumed was "a reputable American company" that he would not lobby government or "attempt to sell confidential or privileged information arising from my time in government". He said he had not broken any rules.
Lib Dem leader Nick Clegg told BBC One's Politics Show the story "just beggars belief" and illustrated the need for "reform of the whole rotten system from top to bottom".
Senior Labour figures were also quick to condemn their former cabinet colleagues, with Chancellor Alistair Darling saying the situation was "ridiculous" and asking on BBC One's Andrew Marr programme: "What on earth did they think they were doing?"
Foreign Secretary David Miliband told Sky News Sunday Live he was "appalled" by the apparent actions of his former colleagues, saying "there is absolutely no room for anyone to trade on their ministerial office".
Labour said it now wanted a statutory lobbying register, which would list details of meetings between lobbyists and decision-makers - something called for last year by the Commons Public Administration Committee to increase transparency, but rejected at the time.
The Conservatives have said they would create a lobbying register "if necessary" - and would rewrite the ministerial code so ministers are banned from accepting lobbying jobs for two years after they leave office.
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