Mr Patten is the threat to peace in Northern Ireland

In private Peter Mandelson has shown himself to be fully aware of the Patten report's failings

On Saturday David Trimble expected the Unionist Council meeting to be over by quarter past one, so he reserved a table for lunch at Tatu's on the Lisburn Road. By quarter past one, Unionist party officials were negotiating to extend their booking of the Waterfront Hall. It was not clear whether Mr Trimble would get any lunch, or whether he would still be leader of the Ulster Unionist's when the meeting closed.

On Saturday David Trimble expected the Unionist Council meeting to be over by quarter past one, so he reserved a table for lunch at Tatu's on the Lisburn Road. By quarter past one, Unionist party officials were negotiating to extend their booking of the Waterfront Hall. It was not clear whether Mr Trimble would get any lunch, or whether he would still be leader of the Ulster Unionist's when the meeting closed.

During the day, most commentators expected him to lose, and at various stages that was also his own assessment. Not that this worried him; Mr Trimble will not stoop to conquer his party. But prevail he did, even though the speeches seemed to be going against him. He won because of thequiet people, who sat and listened patiently before voting to sustain his leadership. He made it to Tatu's for a late lunch at teatime.

The Good Friday Agreement will be lucky to make it until the next Good Friday. Despite Mr Trimble's victory it is still beset by fundamental difficulties. Mr Trimble himself is quite prepared to bring about the collapse of the new devolved institutions, and expects that this will probably happen. Equally, most of those who voted for him on Saturday did not do so because they want peace at any price, but because they trust him to bring down the executive if that becomes necessary.

Mr Trimble is determined to ensure that, if it does occur, the collapse will be on Unionist terms. That was his sole reason for resisting the calls for a Christmas deadline on decommissioning. During the negotiations to reconvene the executive, there was agreement on a June 2001 deadline. Decommissioning cannot be done overnight, however, and back in May, General de Chastelain, in charge of monitoring, said that if there was no movement by March there would be no decommissioning by June.

That is why Mr Trimble favours a March deadline. He could then announce to the world that though his party had been prepared to implement the Good Friday Agreement - as modified by subsequent Unionist concessions - Sinn Fein was intransigent. It was to blame for its collapse. This would be a strong case. Undoubtedly, it would not play as well as it ought to; world opinion will find any excuse to deny Ulster Unionists a fair ration of credit. But it would at least give the Unionists a chance of taking the moral high ground.

That much-disputed region will see a further contest this week. As part of the deal that brought its ministers back to the executive, Sinn Fein was supposed to be in regular contact with General de Chastelain. It has made one phone call since May. But Mr Trimble has a sanction. As First Minister, he signs the invitations entitling other ministers to participate in North/South talks; there is due to be a session on Friday. Mr Trimble has announced that Sinn Fein ministers cannot participate unless they have spoken to the General.

One vague phone call would earn them their entrance ticket, but the world would then know that they had been obliged to do what Mr Trimble told them. Sinn Fein hates it when their supporters - or they themselves - are reminded that the Unionists and the British still have power in Northern Ireland. It is also under some pressure in its own heartlands. The provos recently felt it necessary to murder the Real IRA's commander in Belfast, and that is unlikely to be the last such incident.

In its refusal to truckle to Trimble - as it will no doubt describe its failure to keep its word - Sinn Fein will probably be able to rely on support from its allies in Dublin and in the SDLP. There seems no limit to Dublin's moral shoddiness or Seamus Mallon's melodramatics. So forget January; the new devolved institutions could be under siege by the end of this week, for David Trimble will not give way - unless Peter Mandelson can transform private statements into public policy.

This difficulty arises over the Patten Report on the RUC. Ninety per cent of that document was uncontentious. But the other 10 per cent was damaging and offensive. Damaging, because proposals for local political involvement and lower standards for the RUC Reserve could have sabotaged the force's operational capability. Offensive, because the RUC is to lose its name and insignia: and doubly offensive, because of the report's language.

Chris Patten has been known to write competent English. Yet his document is drafted in a banal, ungenerous officialese, which might just be adequate for an enquiry into paper-clip stocks. Over the past 30 years, thousands of RUC officers have been injured and 307 of them have been killed in action. They made those sacrifices to stand up to terrorism: to stand up for peace, freedom and decency. They deserved better than to have their name and insignia dishonoured.

Peter Mandelson understands this. In private, he has shown himself fully aware of the report's failings. But - as he has often complained - Number 10 will not allow him to make the concessions that he would wish to. Downing Street has its eyes on Washington and Dublin, not on Ulster. So Mr Mandelson finds himself obliged to implement measures that he knows to be flawed.

This does not endear him to Unionists. It also undermines a central element of the Government's long-term strategy. From the outset, a number of senior officials never believed that the IRA would decommission. The hope was that peace and the passage of time would have swayed Unionist anxieties; that with every passing month in which the guns remained silent while the new devolved institutions began to work, the decommissioning issue would lose its potency.

Despite or because of its cynicism, this was not an entirely unrealistic hope. But events have turned out otherwise, for two reasons. First, by "peace", most Unionists meant rather more than the absence of a terrorist war, and there is too much evidence that the paramilitaries are still powerful. Unionists, and not only Unionists, assumed that peace would bring the restoration of law and order and not the increasing mafia-isation of Ulster society.

Second, the Unionists were told that Good Friday would bring local democracy - then the Patten Report brutally reminded them of that Democracy's limitations. Changes that they abhor are being forced on them by ministers who would rather do otherwise, and there seems to be nothing that they can do.

If the Patten Report had been a reasonable document, the Unionists might have eased up on decommissioning. If there had been decommissioning, they might have contained their resentments over Patten. But they cannot be expected to give way on both.

For the moment, peace staggers on. But it is impossible to see how the institutions that were meant to sustain that peace can survive much longer. Despite Saturday's victory, David Trimble has little freedom of manoeuvre; Chris Patten has seen to that. Nor would Mr Trimble necessarily wish to manoeuvre. He knows that he has gone the extra mile for compromise, again and again. He is not prepared to purchase compromise at the price of dishonour.