Sir Malcolm Rifkind has announced he is to step down at the General Election after cash for access revelations.
The Tory MP has also resigned from his role of chairman of the Intelligence and Security Committee after pressure over the lobbying scandal intensified.
In a statement Sir Malcolm, who became an MP in 1974, said it was unfair to friends and colleagues in Kensington for him to continue to remain the candidate for the General Election but added the allegations against him were "contemptible".
He said: "This is entirely my personal decision. I have had no such requests from my constituency association but I believe that it is the right and proper action to take.
"As regards the allegations of Channel 4 and the Daily Telegraph I find them contemptible and will not comment further at this time.
"Although I will retire from Parliament I shall continue my public and political life and am much looking forward to doing so over the years to come."
The MP for Kensington had been due at the regular ISC meeting this morning but admitted that the committee could be "distracted or affected by controversy" and that it would be better for him to step down.
Moments before he announced his resignation, Sir Malcolm was involved in a testy exchange with a Sky News reporter during which he told him to "mind his own business" and accused him of being "childish".
TheTory MP tried to laugh off the episode in an exchange with a woman on the other side of the road who shouted back: "You won't be doing that again will you."
His position at the helm of the influential committee had become increasingly untenable after former chairman Kim Howells said it would be "very difficult" for him to stay.
The Prime Minister had not offered Sir Malcolm his confidence following revelations that he had been secretly filmed telling reporters posing as a Chinese firm he could offer "useful access" to British ambassadors across the world.
He also said he could write to ministers for information without naming the client.
A Conservative spokesman said: "Sir Malcolm has had a long career of distinguished service both to the Conservative Party and the country.
"We respect and support his decision to stand down."
Sir Malcolm has referred himself to the parliamentary standards watchdog but told Sky News on Monday he intended to fight the allegations, insisting he had broken no rules.
Labour grandee, Jack Straw, was also caught by the newspaper sting boasting about working "under the radar" in a £60,000 consultancy role for a commodities company for whom he claimed to have altered EU regulation and Ukrainian law.
He has also referred himself to the watchdog, denying wrongdoing, but had already announced he would stand down as MP at the General Election.
The Labour leader Ed Miliband described the incident as "disturbing".
Some had assumed Mr Straw would move into the House of Lords but Labour sources say that could not happen while an investigation is ongoing. The MP agreed to be suspended from the Labour party.
