The Government has been urged to commit funding to policing in Northern Ireland rather than pursue a "fanciful" investigation unit to examine Troubles-related killings.
US diplomat Dr Richard Haass proposed two new bodies, which included an Historical Investigations Unit (HIU) in place of the Police Service of Northern Ireland's Historical Enquiries Team (HET) and an Independent Commission on Information Recovery.
But Ian Paisley Jr (North Antrim) told the Commons the existing cheaper arrangements are expected to have a £60 million shortfall starting in 2015, while there was also a £36 million shortfall on security.
The Democratic Unionist Party MP told Northern Ireland Secretary Theresa Villiers: "You said in your statement it was disappointing it didn't prove possible to reach an agreement on an historical investigations unit to take the place of HET.
"How will you try to fund such a unit with its panoply of lawyers and additional experts when there is a shortfall of £60 million starting in 2015 for the current arrangement, which is the cheaper option, and when there is another shortfall of an additional £36 million generally on security.
"Will you commit now to finding the money to allow the police to function for the next five years rather than pursue this fanciful idea of an historical investigations unit?"
Ms Villiers replied: "I think you are right to raise the issue of cost. That is something that would need to be resolved in the event of an agreement. As I've said, the UK Government would primarily expect the Northern Ireland executive to fund that from within the considerable resources provided via the broad grant.
"We'll obviously consider any application for a top-up funding to that but when we have to deal with a deficit of the gravity that we do it does make it difficult to commit to additional funds at this stage."