Bruce Anderson: The Real IRA has clarified Mr Blair's choices in Ulster

'Thursday's bomb should remind the Prime Minister that it is impossible to compromise with terrorists'

Internal links

IRA will put its weapons 'completely beyond use'

Guns concession is a chance to rip up the script

Trimble faces a lot of work to persuade his party

The paramilitaries' hidden weapons

Bruce Anderson: The Real IRA has clarified Mr Blair's choices in Ulster

Yet another Ulster deadline is now imminent, with no sign of progress. It is fortunate that this deadline's approach was not heralded by deaths in London, but bombs can simplify issues and clarify moral choices.

It is not yet clear whether the Real IRA (RIRA), which was responsible for Thursday night's bomb in Ealing, West London, merely botched its warning message or whether it did so deliberately in the hope of killing large numbers of people. Whether or not it intended to commit murder, its primary purpose was not homicidal but political.

RIRA was sending a double warning, to the British Government and the Provisional IRA. It was telling London that there would be no point in basing hopes on Gerry Adams. Even if the Provos handed over their weaponry, RIRA would retain its.

But there was also a message for Mr Adams: a reminder of the history of the republican movement (not that he needs one). In large measure, the 20th-century history of republicanism is one of splits and strife. A group of former gunmen will decide that they have achieved enough of their objectives to enable them to renounce violence in favour of democratic politics. But many of their associates disagree and signal their refusal to give up guns by turning them on their former colleagues, whom they see as traitors. Michael Collins was the most famous victim of this process; there were hundreds of others.

In three decades of terrorism, the Provos have already fought three vicious little turf wars against republican rivals, all of which they won. But RIRA would be a much more considerable opponent, for it would win many adherents from within the Provos' ranks. That is the principal reason why the Provos have not moved against RIRA already. The Provos could not be certain of winning.

Mr Adams is not a closet RIRA supporter; he is now ready for the parliamentary road. Over the past two or three years, his political wing, Sinn Fein, has made significant political advances in Ulster and the Republic. In the North, Sinn Fein has overtaken the SDLP. John Hume, whose health is uncertain, is presiding over a dying party, while Sinn Fein seems to have an endless supply of young militants. Until 1997, the SDLP held West Belfast. Martin McGuinness has turned it into a safe Sinn Fein seat, and he has 19 offices in the constituency. If there were fresh elections for the Northern Ireland Assembly, Sinn Fein would probably be returned as the second largest party, while the SDLP would be reduced to little more than insignificance.

In the South, an election is due next year. Most observers expect Shin Fein to win around six seats, though that could prove an underestimate. The present Dublin political establishment has been discredited by a series of corruption scandals, whereas Mr Adams and Mr McGuinness are widely seen as romantic figures. Sinn Fein is also building up a network of intimidation and favours in working-class Dublin, filling a vacuum created by the decline of the traditional parties.

These mutually reinforcing electoral successes in the North and the South have enhanced the prestige and living standards of Mr Adams. Comfortable travel, the plaudits of the naive and the credulous, a general reluctance to check his hands for bloodstains; all this is a much more enjoyable mode of life than wary journeys between dubious safe houses.

But some, at least, of his comforts should now be under threat, for democracy has an entrance fee. The small print on the Good Friday Agreement is often ambiguous; sometimes deliberately so, sometimes because it was drafted by tired officials in the small hours. But the moral thrust is clear. The Provos were to be admitted into government, but only if they decommissioned their weaponry. In a phrase widely used at the time: "No guns, no government.''

Nearly three-and-a-half years later, not one single weapon has been decommissioned. In response to the Provos delays and evasions, the Unionists have shown themselves capable of patience and restraint on a scale that no one would have believed possible. But there are limits, as David Trimble made clear to Tony Blair during their recent talks at Weston Park.

Mr Blair gave an impressive performance during those negotiations, but there was one problem. He still appeared to believe that by talking and arm-twisting he might find an acceptable way to blur and fudge the issues. He did not appear to realise that it was time for a fundamental moral choice. In that respect, Thursday's bomb may have helped him think more lucidly.

The whole incident ought to remind Mr Blair that there is no place in democratic politics for those who seek a dual mandate: the ballot box and terrorism. No democratic politician could, or should, be expected to do business with political rivals who might respond to the inevitable frustrations of democratic politics by reverting to terror.

The document which the British and Irish governments produced after Weston Park was not as bad as many Unionists feared. There was no attempt to impose wholesale concessions on Mr Trimble's party in the hope of bribing the Provos into carrying out their undertakings. But there is a perennial weakness which English politicians are prone to display in such situations: a rooted belief that the answer must lie in splitting the difference.

On this occasion there was no difference to split. The Unionists had already agreed to concessions which many of them found repugnant. Above all, they were happy to sit down in an executive and work with the leaders of paramilitary organisations which had murdered some of their friends and constituents.

But the IRA has clearly persuaded itself that if it remains obdurate, the British and Irish governments will never face it down. This assessment may be offensive. It has not yet been proved to be erroneous.

In the aftermath of Good Friday, Mr Blair gave the Unionists an assurance. He told them that if the IRA refused to decommission, he would amend the legislation so that the Northern Ireland Executive could remain in being without Sinn Fein. At that stage, no one thought that Mr Blair would ever have to keep his promise. It was widely assumed that the IRA would decommission, at least to some extent. This might, indeed, have happened if the British government had kept up the pressure after Good Friday and maintained the momentum which the peace process had in its early stages.

But that momentum has long since been lost. The Provisionals have obviously concluded that they will always be able to evade pressure to decommission. It is now time for Mr Blair to prove them wrong and to keep his word. Thursday's bomb ought to have reminded him and everyone else that there comes a point at which it is impossible to compromise with terrorists. Governments that show weakness encourage terrorism. If Mr Blair were to allow the Northern Ireland executive to founder because the Provos refused to disarm, he would be displaying abject weakness. Others would suffer the consequences.