The Conservative Party has suspended the whip from former foreign secretary Sir Malcolm Rifkind, and a party disciplinary committee will investigate cash-for-access allegations resulting from an undercover sting operation.

Sir Malcolm, who chairs the parliamentary committee which oversees Britain's intelligence agencies, was one of two senior parliamentarians secretly filmed by reporters posing as representatives of a fictitious Hong Kong-based firm seeking to hire senior British politicians to join its advisory board.

The veteran MP is said to have claimed that he could arrange "useful access" to every British ambassador in the world because of his status, while Labour's former foreign secretary Jack Straw boasted of operating "under the radar" to use his influence to change European Union rules on behalf of a commodity firm which paid him £60,000 a year.

Both men have denied any wrongdoing and have referred themselves to the Parliamentary Standards Commissioner. Mr Straw has suspended himself from the Labour Party while he fights to clear his name.

Following a meeting between Sir Malcolm and Tory Chief Whip Michael Gove this morning, a Conservative source said: "The Conservative Party has suspended the whip from Sir Malcolm Rifkind - effective immediately.

"A disciplinary committee of the party will be convened to investigate his case."

Mr Cameron declined to say whether he believed Sir Malcolm should stand down from his ISC position during his suspension from the Parliamentary Conservative Party, stressing that the 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," said the Prime Minister.

Answering questions following a speech in Hastings, East Sussex, Mr Cameron described the allegations as "very serious matters" and said it was "right" that both MPs had referred themselves to the Standards Commissioner.

Ed Miliband wrote to the Prime Minister urging him to follow Labour's lead by banning his MPs from taking directorships and consultancies, and floating proposals for a cap on outside earnings.

Labour MPs and prospective parliamentary candidates have already been warned that the party's rulebook will be changed to stop them holding such posts after the May general election - a commitment Mr Miliband confirmed will be in the Labour manifesto.

And the Labour leader also revealed he is consulting on legislation to put the ban into law for all MPs and to impose a cap on outside income similar to that in place for members of Congress in the US, who may earn no more than the equivalent of 15% of a minister of state's salary on top of their pay as lawmakers. Party sources stressed that no figure has been set on the proposed cap, but the US example suggests that a level of around £5,000-£15,000 a year may be under consideration.

Mr Miliband told the BBC: "We've got to settle this issue of second jobs once and for all so we remove any suspicion that MPs are working not for their constituents' interests but someone else's interests."

But the Prime Minister rebuffed Mr Miliband's proposals, saying: "On the issue of outside jobs and outside interests, I think we do have very clear rules and they need to be properly enforced.

"I don't favour a complete ban on all outside jobs or interests. I think Parliament is enriched by the fact that we have, whether it's a GP doing some time in a practice, a minister who's actually an obstetrician ... or people who have small businesses or sit on other businesses and draw some interesting experiences from that that they can bring to the House of Commons.

"What I see from the Labour proposal is actually not outlawing outside business interests, but putting a new set of rules which, for instance, would allow someone to work as a trade union official but wouldn't allow someone to run a family shop or a family publishing business or suchlike. I think that doesn't make sense.

"Enforce the rules - total transparency - and demonstrate to people that people in Parliament are there to work for them, serve their communities and serve their country.

"These are serious issues. They need to be properly looked into and I'm sure they will be."

Mr Cameron's official spokesman said the Prime Minister was due to speak with Mr Gove about Sir Malcolm's case following this morning's meeting, though it was not immediately clear whether this conversation had taken place by the time the suspension was announced.

Both Sir Malcolm and Mr Straw took to the airwaves this morning to defend themselves against allegations arising from the undercover operation by the Daily Telegraph and Channel 4's Dispatches.

Mr Straw said he was "mortified" to have fallen for the sting, while Conservative Sir Malcolm said he was "irritated and angry" and insisted he had "nothing to be embarrassed about".

The undercover reporters met Sir Malcolm at the fictional firm's office in London's Mayfair in January, where he is said to have told them he could meet "any ambassador that I wish to see" in the capital.

"They'll all see me personally," he said. "That provides access in a way that is, is useful."

In a second meeting, Sir Malcolm was said to have suggested that he would be willing to write to ministers on behalf of the company without declaring the name of the firm.

During the meetings, Sir Malcolm is said to have described himself as being "self-employed", saying "nobody pays me a salary". He is said to have discussed his usual fee for his services as being "somewhere in the region of £5,000 to £8,000" for a half a day's work.

Mr Straw met the undercover reporters at his office in the Commons - a potential breach of Commons rules - where he is said to have explained how he helped ED&F Man - a commodities company with a sugar refinery in Ukraine - change an EU regulation by meeting officials in Brussels for "under the radar" talks.

He was quoted saying he used "charm and menace" to convince the then Ukrainian prime minister to change laws on behalf of the same firm.

The veteran MP - who is stepping down in May after 36 years representing Blackburn in Parliament - reportedly explained that he normally charges a fee of £5,000 a day for his work. He made clear he would not take on the role while he remained an MP, but is said to have suggested that he could be more helpful to the company if he became a peer, as different rules apply.

Kensington MP Sir Malcolm, who first entered Parliament in 1974 and served for more than a decade in the cabinets of Margaret Thatcher and John Major - dismissed allegations of wrongdoing as "unfounded" and vowed to fight them "with all my strength".

He told the BBC Radio 4 Today programme: "Many ex-ministers, former chancellors, home secretaries, prime ministers, as well as other people, have served on advisory boards ... This is something which Parliament has said is acceptable."

Sir Malcolm said there were "about 200" MPs who had business interests and insisted many members of the public did not want "full-time politicians".

"If you are trying to attract people of a business or a professional background to serve in the House of Commons, and if they are not ministers, it is quite unrealistic to believe they will go through their parliamentary career being able to simply accept a salary of £60,000," said Sir Malcolm.

"That sounds a lot to a lot of people earning less than that but the vast majority of people from a business or professional background earn far, far more than that. If they are told they have to choose one or the other they just won't come to the House of Commons at all and Parliament will lose their skills."

Sir Malcom claimed he had offered to appear on the Channel 4 programme to answer the allegations but "they refused to allow me".

Asked if he would be embarrassed when the programme airs this evening, he replied: "No, I'm going to be hugely irritated and angry because I have got nothing to be embarrassed about. Every single thing I said to these people I would have been willing to say on television or to you if you had put the same questions to me at the time."

Sir Malcolm said he would "certainly not" stand down as chairman of Parliament's Intelligence and Security Committee, adding: "None of the matters, even that the Telegraph are alleging, or complaining about, are remotely to do with intelligence and security."

Mr Straw said he had agreed to suspend himself from the Parliamentary Labour Party and refer himself to the Parliamentary Commissioner despite insisting he has done nothing wrong "because of the way this appears".

He told Today: "I'm mortified by the fact that I fell into this trap ... Inevitably, if you have what you think is a private conversation where you trust the person, or people, you are talking to, you use language not that's necessarily wrong but could be taken out of context."

Mr Straw insisted he had been "absolutely scrupulous" in observing all the rules, including on outside interests, and stressed that he had not reached any agreement to work with the fictitious company.

"This discussion with this bogus Chinese Hong Kong company was not about what I was going to do as a Member of Parliament. It was all about what I might do once I had left the House of Commons on May 7," he said.

Asked why he had not waited until after the election, he replied: "Well, I should have done, is the answer. It would have saved a fantastic amount of time and trouble ... Of course I very much regret the fact that I saw these people."

His reference to working "under the radar" was intended to reflect the fact that negotiations with the EU were better conducted through "polite and quiet and forensic" private conversations than by "shouting" in public, he said.

When former Cabinet colleagues Stephen Byers, Geoff Hoon and Patricia Hewitt were caught up in a similar sting in 2010, Mr Straw said there was "anger and incredulity" among Labour MPs over "their stupidity in allowing themselves to be suckered in a sting like this". He said he now accepted that his comments had been "too strident".

Former prime minister Tony Blair came to the defence of Mr Straw, who served as home secretary, foreign secretary and leader of the Commons in his administrations.

Mr Blair said: "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."

Speaking at an event in south London, Deputy Prime Minister Nick Clegg said the cash-for-access claims felt like "Groundhog Day - this keeps coming round".

He said that "whether there is individual wrongdoing or not, the cumulative effect is to deepen public scepticism about how politics operates and that's a great shame for anyone who believes in the quality of our democracy.

"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."

Ukip leader Nigel Farage said it was "very questionable" whether Sir Malcolm should continue in his ISC role.

"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.

Responding to Mr Cameron's defence of MPs having second jobs, Labour's shadow leader of the Commons Angela Eagle said: "It is deeply regrettable that the Tories have rejected important measures which would help restore trust in politics.

"David Cameron once promised change but now defends a discredited status quo. Faced with big challenges, David Cameron's leadership has again been found wanting."

Shadow leader of the House Angela Eagle said Mr Straw had "serious questions" to answer.

She told BBC Radio 4's World At One: "I think Jack's got important and serious questions to answer. There is a process for doing that. I don't want to second-guess that."

Asked if Sir Malcolm should step down as chairman of the ISC, she replied: "I think it is very important that Sir Malcolm takes a good look at the circumstances he finds himself in and makes a judgment on that."

Scotland's First Minister Nicola Sturgeon said: "These allegations are awful, appalling and shocking. They really must be very robustly investigated. All of this - cash for access, politicians whose outside interests compromise their integrity as parliamentarians - all of this conjures up the very worst of the Westminster establishment all over again.

"People will be appalled by this and it is yet another reason why I think the Westminster establishment - the cosy Westminster consensus that seems to see politics being about progressing the interests of the few rather than the many - that's what needs shaking up, that's what needs turning on its head."