Ex-foreign secretary Sir Malcolm Rifkind is standing down as an MP after being secretly recorded apparently offering his services to a private firm for cash.
He was suspended from the Conservative party on Monday following accusations that he was prepared to accept money in return for buying influence in parliament.
Labour grandee Jack Straw was suspended by his party after getting caught in the same sting by Channel 4's Dispatches and the Daily Telegraph. Both MPs have strongly denied any wrongdoing.
Rifkind, who holds his Kensington seat with a 8,616 majority, insisted he had not been forced out by his local Tory association.
In a statement, he said:
I had intended to seek one further term as MP for Kensington, before retiring from the House of Commons. I have concluded that to end the uncertainty it would be preferable, instead, to step down at the end of this parliament.
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.
Rifkind also resigned as chair of the intelligence and security committee, which oversees the work of MI5, MI6, and GCHQ.
He insisted that "none of the current controversy" was relevant to his role.
"However, I have today informed my colleagues that while I will remain a member of the committee, I will step down from the chairmanship," he said.
"The committee is due to be dissolved in little over a month with the prorogation of parliament for the forthcoming general election. The main substantive work which needs to be completed will be the publication of our privacy and security report during March.
"I do not want the work of the committee and the publication of the report to be, in any way, distracted or affected by controversy as to my personal position."