The Leader of the House of Commons has agreed to pursue an investigation over whether a former Westcountry MP was on the payroll of communist spies.
Conservative colleagues have said they are "shocked" by new information that Ray Mawby, the late MP for Totnes, funded a gambling habit by selling information to the Czechs for £100 a time.
But the current incumbent of the Totnes seat, Conservative MP Dr Sarah Wollaston, has obtained an agreement that the matter should be properly investigated to put both sides forward.
Czech Security Service files reveal Mr Mawby was in its pay for a decade, up until 1971, according to the BBC.
He supplied spies with a floor plan of the prime minister's Commons office, lists of parliamentary committees, information about colleagues and a supposedly confidential parliamentary investigation into a Conservative peer, it found.
Speaking at business questions in the Commons yesterday, Dr Wollaston demanded a full debate on setting up an inquiry.
She said: "These very serious allegations, amounting to treason, need to be fully investigated, but also fairly investigated because Mr Mawby is not here to defend himself and it is in none of our interests to have trial by media."
Leader of the House Sir George Young, who served in the Commons alongside Mr Mawby between 1974 and 1983, agreed that it was "imperative" the other side of the story is put forward, and pledged to make further inquiries.
Former North Cornwall MP Paul Tyler, now Lord Tyler, was Mr Mawby's Lib Dem opponent in the 1966 general election and described the allegations as "mind-boggling".
Mr Mawby and his wife lived "modestly" near Newton Abbot, Lord Tyler said, and were treated "shamefully" by more "snobbish" Totnes Tories because of his working-class links.
Lord Tyler said: "I suspect that he wasn't a very useful spy. Certainly, his one year ministerial career as assistant postmaster general (1963-4) was a disappointment all round."
He recalled Mr Mawby quoting "completely nonsensical" figures during a television interview, and said: "Perhaps the Czechs too realised that he wasn't very reliable because they seem to have dropped him soon after."
Heather Burwin, president of the Totnes and District Conservative Association, said the party had been "delighted" that he stood as a Conservative candidate because he was the first trade union Tory MP – but she believes his performance proved disappointing, and led to his de-selection.
Mr Mawby, who served as MP for Totnes from 1955 until he was deselected in 1983, began accepting "loans" while playing roulette and other games, the files show.
He later went on to accept payments, usually for £100 a time, for information and was given the codename Laval.
Mr Mawby became assistant postmaster general and a junior minister in 1963.
His handler feared the promotion could end their arrangement as it meant a salary increase of £2,000 a year, but the MP continued the arrangement, the files claim.
As well as supplying information about the layout of the PM's parliamentary office, he provided details about its security arrangements, documents say. Notes written by his Czech handler claim he had also promised to ask Parliamentary questions for them.