Former British prime minister Tony Blair may be called before a House of Commons inquiry to give evidence about the decision to tell IRA "on-the-runs" they were not wanted for prosecution.

The decision was taken by the Commons' Northern Ireland Affairs Committee, which has been angered by the curbs placed by British prime minister David Cameron on an inquiry to be conducted in private by a judge.

The judge's inquiry, which can look into the administration of the letters-of-comfort scheme, but not the policy decisions behind it taken by senior politicians, is "too narrow", complained the committee's chairman, Conservative MP Laurence Robertson.

"There is also concern that evidence will be taken in private during that inquiry, when, in fact, it is the secrecy of the on-the-runs scheme which has contributed greatly to the problems," he told The Irish Times .

The controversy erupted after the central criminal court in London ruled Donegal man John Downey could not be prosecuted for the 1982 Hyde Park bombings because he had been told (wrongly) he was not wanted by British police.

'Who authorised it'
MPs will question senior politicians, Mr Robertson said. "We want to know how it was authorised, who authorised it, we are going to go back to the very start; how the list was drawn up, everything. Also, the Royal Pardons."

Equally, he said, the committee will inquire into why the British government continued to issue letters – 38 of them – after it came to power in 2010 and after justice and policing powers were devolved to Stormont.

Final terms of reference will be drawn up in coming days, he said, though it is so far unclear as to when evidence could begin to be taken – though Mr Robertson expressed some hope that it could begin within a fortnight.

Questioned about the likelihood Mr Blair could be called, he said: “We have still got to look at the list of witnesses, but I would imagine so .”