The Social Democratic and Labour Party reacted angrily by warning it would not return to the inter-party talks until the Government has spelt out its 'deal' with the Unionists.
John Major and the nine Unionist MPs who voted with the Government denied there had been a deal. 'Nothing was asked for, nothing was offered and nothing was given,' the Prime Minister told the Commons.
But ministers confirmed that the balance between the Unionists and the demands of the Dublin government over the Anglo-Irish agreement had swung back in favour of the Unionists.
'The Prime Minister has reasserted his authority over the Northern Ireland Office,' one minister said.
Although there is no detailed package of concessions, the change of tone by London will alarm the Dublin government. Ministers there were guarded in their response, playing down the importance of the Tory-Unionist axis.
Dick Spring, the Foreign Affairs minister, was closely monitoring events in London throughout the day, but stressed that he had no indication of whether an accord had been agreed with the Unionists.
Dublin is now expected to seek a clear statement from London on how it intends to approach the government of Northern Ireland in an effort to glean what an obligation to the Unionists may entail, and whether this may shape British policy over the rest of Mr Major's term of office.
John Taylor, one of the Ulster Unionists who voted for the Government, said: 'It's not a question of pay-back time. It's a question of the Conservative Party and the Unionist Party working more closely with each other to maintain the Union of the United Kingdom.'
The Unionists may get a Commons select committee on Northern Ireland, which could be given powers to review Northern Ireland legislation. That was put on the agenda by Brian Mawhinney, the former Minister of State for Northern Ireland, some years ago. But the prize of a commitment to the Union they believe they have won is potentially more far-reaching.
Hours before Thursday night's votes, David Trimble, one of the Ulster Unionist leaders, held talks lasting 90 minutes with Sir Patrick Mayhew, the Secretary of State for Northern Ireland. Mr Major also telephoned James Molyneaux, leader of the Official Ulster Unionists.
'They can have anything they want, short of the Anglo-Irish agreement, which they know we cannot abandon,' one senior Conservative Party source said.
Before they voted, the Ulster Unionists issued a statement which said: 'Our basic commitment to the Union must take paramount place. The Prime Minister has clearly placed himself in the forefront of the fight for the Union.'
The shift in the Government's attitude was signalled in the days leading up to the vote. Mr Major denounced as a 'betrayal' of the people of Northern Ireland a draft Labour policy paper for the last election raising the possibility of joint Anglo-Irish sovereignty over Ulster under a Labour government.
Sir Patrick then publicly repudiated the idea of joint sovereignty over Ulster when it was floated by Mr Spring at an Anglo-Irish conference in London.
The Unionists claimed that they had been driven into the division lobby with the Government by the policy paper prepared by Kevin McNamara, Labour's spokesman on Northern Ireland.
Mr Taylor said the Labour Party was not prepared to work with the Unionists to strengthen the Union.