Tory MP Sir Malcolm Rifkind is to step down as an MP at the General Election and has also resigned as chairman of the Parliamentary Intelligence and Security Committee, he said.
The problem is that it is a very difficult argument to make - but there is an argument to be made for MPs to be allowed outside interests on the grounds that it attracts a slightly greater breadth of professional people into the House of Commons. MPs also say they are not paid enough. Well that really depends on who you compare them to I suppose. But the difficulty for them is really simple.
It is not like it is the world's biggest secret what MPs are paid. It's right there on the tin when you take the job. More to the point, when all of us send our MPs to the Commons, it is really clear that we want them to represent our interests.
We do not particularly want them to represent the interests of company X or company Y - for any reason. That's the reality. That's why these scandals will keep recurring until, I am afraid, MPs are banned from taking on any outside consultancies, and it doesn't look like that's about to happen.
A former chairman of the Committee on Standards in Public Life has criticised Malcolm Rifkind and Jack Straw for being caught out by a sting operation at a time when public trust in MPs is "very low".
Sir John Alistair Graham said that Mr Rifkind would have had to let ministers know if he was working on behalf of a company when making enquires, and raised questions over whether Jack Straw's researcher did "private work" on his behalf in the House of Commons.
David Cameron has said that MPs being paid to lobby is "not acceptable" adding that it was right that Jack Straw and Malcolm Rifkind have referred themselves to the Parliamentary Commissioner,
Speaking in Hastings, the Prime Minister said: "...I think it's also right that in both cases, while that happens, the party whip should be suspended. That is what will happen with Sir Malcolm Rifkind as well as with Jack Straw.
"In Sir Malcolm's case, he is still a candidate at the next election, so there will be an immediate disciplinary inquiry by the Conservative Party to look at this case."
Former prime minister Tony Blair came to the defence of Jack Straw, who served as home secretary, foreign secretary and leader of the Commons in his governments, over the cash-for-access row.
I have known Jack for over 30 years. He is a byword for being a hard-working constituency MP and parliamentarian. I can think of no-one who has more dedicated himself to public service.
I am really sorry he has been caught up in a sting operation about a job offer after he retires from Parliament. It is typical of Jack that as soon as he was alerted of the sting against him he immediately contacted the Parliamentary Commissioner for Standards and asked her to investigate the case. I hope that the Commissioner will clear his name as soon as possible.
Ukip leader Nigel Farage said it was "very questionable" whether Sir Malcolm Rifkind should continue in his role as Intelligence and Security Committee chairman in wake of cash-for-access claims.
"I'm not surprised he has been suspended and I would have thought it very questionable whether he can hang on to any other senior positions at all," Mr Farage said at a campaign event in Rochester, Kent.
Nick Clegg said the cash-for-access claims involving former foreign secretaries Jack Straw and Sir Malcolm Rifkind felt like "Groundhog Day".
"This keeps coming round, " said the Deputy Prime Minister. "Whether there is individual wrongdoing or not, the cumulative effect is to deepen public scepticism about how politics operates.
"My own view is all political parties would be well advised to immediately after the next general election get together and have a look on a cross-party basis whether the rules need to be changed."
David Cameron has declined to say whether he believes Sir Malcolm Rifkind should stand down as chair of the Intelligence and Security Committee over cash-for-access claims.
Rifkind has been suspended from the Parliamentary Conservative Party while a probe into the claims take place, but Cameron stressed that the ISC chairman was selected by the committee's members and not the Prime Minister.
"I can't interfere with that - it is a matter for the committee and the House of Commons," he said.
The Conservative Party has suspended the whip from Sir Malcolm Rifkind and will convene a disciplinary committee to investigate his case, a party source has said.
Jack Straw said his involvement in a cash-for-access row was "not how I expected to spend my last weeks in Parliament".
The former Foreign Secretary, who will stand down as MP for Blackburn after the general election, reiterated that he had "done nothing wrong".
Straw was secretly filmed by the Daily Telegraph and Channel 4's Dispatches progamme, who have accused him of offering to use his position in return for cash.