The Conservative Party is still threatening to oppose tonight's third reading of the Northern Ireland (Sentences) Bill amid continued Ulster Unionist confusion and division on the issue.
Last night, the party leadership claimed to have won a number of critical concessions from the British government on the Bill enabling a two-year programme of prisoner releases.
At the same time, there were unconfirmed reports that Mr David Trimble, the Ulster Unionist Party leader, would not be at Westminster for tonight's vote, while a majority of his colleagues were preparing to renew their opposition to the measure giving effect to one of the most controversial elements of the Belfast Agreement.
During yesterday's continuing Committee Stage of the Bill at Westminster, ministers signalled two changes to the proposed legislation: one providing that victims should be notified in advance of relevant prisoner releases, and the other giving the Northern Secretary power to seek to revoke a licence, up to the point of release, in the light of any new information about an applicant prisoner or the activities of any organisation deemed to qualify under the scheme.
And the British government was hoping to defuse unionist opposition further ahead of tonight's vote with an amendment to the key Clause 3 of the Bill - effectively linking prisoner releases and co-operation with the International Commission on Decommissioning on the stated objective of the agreement that decommissioning should be achieved over a two-year period.
In a statement last night, Mr Ken Maginnis, the UUP security spokesman, said these amendments - while not stepping outside the provisions of the Belfast Agreement - did "formally legalise" the assurances set out by the Prime Minister, Mr Tony Blair, in his Balmoral speech last month.
And he claimed "the securing of these amendments is a direct result of the sustained pressure applied on government by the Ulster Unionist Party, specifically in respect of the commitments made by the Prime Minister to the people of Northern Ireland".
However, it was not clear if these claimed achievements would see Mr Trimble at Westminster tonight to reverse his position of last Wednesday, when he voted against the Bill.
And his designated spokesman on the Bill, Mr Jeffrey Donaldson, told The Irish Times that "in the absence of amendments which would have created a requirement for actual and ongoing decommissioning to be taking place, I will be voting against the Bill".
In the Commons yesterday, Mr Blair rejected a Tory suggestion that people in the North had voted Yes in the referendum on the basis of "a false prospectus". He had made it clear that the Northern Secretary and the International Commission, in considering prisoner releases, "are bound to have regard to whether decommissioning is taking place".
And while he could not alter the agreement or impose fresh legislative preconditions, Mr Blair said the Bill reflected his Balmoral assertion "requiring full co-operation to implement the provisions of the Belfast Agreement".
Decommissioning, said Mr Blair, "is an essential part of the package".