Leading Ulster Unionist MPs, whose support has been crucial to John Major's survival, last night called for Sir Patrick's resignation over the breakdown of trust with Mr Molyneaux.
Conservative MPs plan to use tonight's meeting of the 1922 Committee of Tory MPs to underline their anger at what some said was a "betrayal" of Mr Molyneaux.
Some of the 1922 Committee's executive privately told Ulster Unionist MPs that they were deeply disappointed by the failure of Sir Patrick to give more convincing assurances in the House.
One disillusioned Tory MP said: "There are a lot of very angry Conservative MPs and I can think of about five who have said they will take their lead from James Molyneaux, not John Major. This is a very serious crisis for the Government. It could lead tototal collapse.''
John Taylor, an Ulster Unionist, confirmed that a Tory MP had told him he would resign from the Government if it went ahead with the leaked proposals for a cross-border body with executive powers.
Mr Taylor said that there was "more concern than ever" after Sir Patrick's assurances to the Commons. "It is clear that Sir Patrick Mayhew is going to impose all-Ireland bodies with executive powers over Northern Ireland and that is joint authority.
"There is clearly a division between [Sir Patrick and James Molyneaux] and there can be little progress unless Sir Patrick resigns," Mr Taylor added.
Anxieties were heightened by Sir Patrick's failure in the House to match assurances given at a private meeting for around 70 Tory MPs by the Prime Minister on Tuesday.Reuse content