A Westminster committee investigating contentious Government letters-of-assurance sent to republican fugitives should consider compelling Sinn Fein to give evidence, an MP has urged.
Democratic Unionist Ian Paisley's call came after the republican party declined an invitation to appear before the Northern Ireland Affairs Committee inquiry into the on-the-runs controversy.
The committee is examining the process agreed between Sinn Fein and the last Labour government that saw around 200 letters sent to republicans informing them UK police were not actively seeking them. A number of fugitives who were being actively sought by the authorities were unable to obtain letters.
Yesterday Stormont's Sinn Fein Deputy First Minister Martin McGuinness announced that senior party Assembly member Gerry Kelly, who had a key role in the scheme, would not be appearing before the committee when it holds evidence hearings in Belfast on Monday and Tuesday.
Mr McGuinness said the party had already co-operated with a separate judge-led inquiry, commissioned by Prime Minister David Cameron, being conducted by Lady Justice Heather Hallett.
Mr Paisley and fellow DUP member of the committee David Simpson MP have heavily criticised Sinn Fein's stance in not attending its hearings.
"Sinn Fein's refusal to fully co-operate with the Select Committee inquiry into the corrupt on-the-runs letters is not surprising," said North Antrim MP Mr Paisley.
"It was (Sinn Fein President) Gerry Adams who said the OTR scheme must be kept 'invisible' or else unionists would have scuppered it.
"However, the Inquiry has powers to compel witnesses and I will asking the Committee to investigate using these powers. Indeed, I trust that this will be the first matter of business."
Upper Bann MP Mr Simpson said the truth about the "immoral" scheme must be brought to the surface.
"That is why it was the DUP that insisted on no stone being left unturned. This matter must be fully investigated," he said.
"SF's approach to this inquiry speaks volumes about their attitude to truth recovery when this is the approach they take to telling the truth about this corrupt scheme. There seems to be a reluctance to be cross examined in public about the matter.
"These letters corrupted justice. Justice should never be time-limited and there must never be anyone who is 'untouchable'. It is vital that wherever evidence can be gathered that this is followed to its conclusion, regardless of where that leads."
The scheme became the focus of intense public scrutiny in Feburary after the collapse of a case against a man accused of the IRA's Hyde Park bomb in 1982 - an attack that killed four soldiers.
The prosecution of John Downey, 62, from Co Donegal, was halted when it emerged he was wrongly sent a so-called letter of assurance informing him the authorities in the UK were not looking for him.
Downey, who was wanted by detectives in London, had denied the murder of the four soldiers.
Yesterday, Mr McGuinness said: "Sinn Fein has clearly outlined our position on the issue of on-the-runs and despite claims to the contrary, neither this process, nor the agreements on which it was based, were secret or hidden.
"However, in the interests of transparency and in an attempt to minimise the damage to the peace process from a growing public controversy, Sinn Fein agreed to participate fully and willingly in the Hallett Review.
"To that end our party president Gerry Adams, Gerry Kelly and myself met with the Hallett review team earlier this week and put Sinn Fein's position on this and other legacy issues on the record.
"We see no point therefore in Gerry Kelly attending the Westminster Select Committee into the issue."
Last night Laurence Robertson, chair of the Northern Ireland select committee, said he was "surprised" at Sinn Fein's decision.
"I am especially surprised that they say they are giving evidence to the Hallett inquiry," the Conservative MP for Tewkesbury said.
"It begs the question 'what is the difference?' and of course there is a big difference - one is in public and the other is in private.
"That is the only difference I can see and that is obviously something that they are uncomfortable with.
"We were giving them the opportunity to put forward their point of view in public. If everything is above board why not come in and discuss it?"