Labour MP Jack Straw has insisted he has done "nothing wrong" after being covertly filmed apparently offering to use his influence in return for money.

Mr Straw and Sir Malcolm Rifkind are facing allegations of being involved in a new "cash for access" scandal following a joint investigation by the Daily Telegraph and Channel 4's Dispatches.

Reporters claiming to represent a Hong Kong-based communications agency called PMR contacted the MPs to say they were seeking to hire senior British politicians to join the company's advisory board.

At one meeting, Mr Straw is alleged to have described how he operated "under the radar" to use his influence to change EU rules for a commodity company which paid him £60,000 a year.

The newspaper reported he claimed to have used "charm and menace" to convince the Ukrainian prime minister to change laws on behalf of the same company.

Sir Malcolm is said to have claimed he could arrange "useful access" to British ambassadors.

He also described himself as "self-employed", and added "nobody pays me a salary".

Both of the MPs have referred themselves to the Parliamentary Commissioner for Standards in light of the claims.

Mr Straw, who has also suspended himself from the Labour Party, told Sky News he was "mortified by the fact that I'd fallen into a trap", and insisted he was discussing what he might do when he stands down as an MP in May.

He said: "If I didn't believe it was morally right I wouldn't have done it at all.

"I'm quite clear that what I've done is morally and ethically right and is also within the rules."

Sir Malcolm told Sky the allegations were "completely unfounded" and vowed to "fight them all the way".

He said: "I wasn't embarrassed by them.

"I was annoyed, very angry, because when your reputation is being attacked that is something you hold dear to.

"I've been in public life for a long time, I know what is permitted, what is proper, and that's what I stick to."

Sir Malcolm, who chairs the parliamentary committee which oversees Britain's intelligence agencies, said he offered to answer the allegations on the programme, but Channel 4 refused.

The Prime Minister's spokesman has refused to say David Cameron has confidence in Sir Malcolm as the head of that committee, Sky's Deputy Political Editor Joey Jones reports.

Sir Alistair Graham, a former standards commissioner, has told Sky News Mr Straw had "some questions to answer" about the use of his researcher in relation to his private work.

However, the MP said Sir Alistair was "stretching it to suggest there has been any impropriety at all".

Labour leader Ed Miliband has written to the PM, calling on him to ban MPs from holding paid directorships and consultancies.

He said the allegations were "disturbing".

Mr Miliband said: "We need a proper investigation of this.

"But I believe we need to go further. Labour candidates standing at the next election will be banned from taking paid directorships or consultancies."