Commons Speaker Michael Martin was leant on by "very senior political sources" to fight efforts to make MPs' expenses more transparent, it was claimed today.

Labour MP Sir Stuart Bell, a member of the ruling House of Commons Commission, said the Speaker, was put under "severe pressure" to launch a doomed High Court challenge against Freedom of Information requests to release details of MPs' allowance claims.

Commons Leader Harriet Harman said it was important to have an "authoritative" legal ruling but denied Mr Martin was "leant on".

Mr Martin became the first Speaker to be forced out of office in more than 300 years earlier this month, partly because he was seen as a roadblock to reform as a result of the expensive and futile High Court challenge.

In an interview with BBC Radio 4's The Report to be broadcast tonight, Sir Stuart said: "The Speaker, unfortunately for him, was caught in this terrible dilemma of trying to meet the requests of the Freedom of Information Act and at the same time trying to say to MPs 'I'm trying to look after your interests'.

"This man, this Speaker of the House of Commons actually failed because he was trying to help his Members of Parliament.

"The Speaker came under severe pressure from very senior political sources that he must appeal this to the High Court."

Challenged about Sir Stuart's claims, Ms Harman told the programme: "I think that it was important that we had an authoritative ruling, a High Court interpretation of what the law was, but also that we were absolutely clear that we were protecting personal addresses."

She added: "When you are the Speaker of the House of Commons you are not leant on by anybody.

"You are authoritative, you are in the position of Speaker and you make your own decisions."

Mr Martin will stand down on June 20, with an election to find his replacement the following day.

Announcing his decision to "relinquish" the post he said he was quitting to maintain "unity" in the Commons.