It was always certain that the policing issue would be critical to a settlement in Northern Ireland and that it would represent heavily contested ground. But it is no exaggeration to say that if it cannot be resolved satisfactorily it will leave the Belfast Agreement holed below the waterline and incapable of advancing as it must. A community in which the police service - the visible symbol of civic authority - is viewed by one section as "ours" and by another as "theirs" cannot fully achieve social cohesion.
The responsibility for getting this one right rests uniquely with Mr Peter Mandelson. In a sense, he inherited other aspects of the peace process as a fait accompli. This is his special task. If he does not succeed in creating the conditions in which the new police service is acceptable to both nationalists and unionists, in which young men and women of both communities will be proud to serve, he will have presided over a dismal and dangerous failure.
There are other, downstream responsibilities too. The political parties in Northern Ireland and indeed the Dublin government will have to be unambiguous in their stances once the Police Bill passes into law and assuming that it fairly meets the criteria and objectives set down in the Patten report. There must be no reserving of positions or each-way betting. If police officers are to commit themselves to the new service they must know that those who hold the authority which the police will represent on the streets are backing them wholly and unequivocally.
The Patten Commission, guided as it was by men and women experienced in the application of policing authority in contested circumstances, spelled out how this could be achieved in Northern Ireland. It is regrettable that the British government should feel itself required to deviate in any way from what Patten set down and it is essential, when Mr Mandelson tables the Police Bill this week, that it is proofed against the criticisms which have been laid against it by Sinn Fein, the SDLP and by the Dublin government. Mr Mandelson's officials have let it be known that he has taken on board a great many of the points raised in recent days and that he believes he can allay any disquiet.
Let us hope so. Mainstream unionism has courageously and imaginatively put its weight behind the Agreement. But it is not entitled to concessions on the policing issue and Mr Mandelson must resist any pressure to give them. He has held firm on the question of title and symbols. But he must be no less firm - and courageous - on the substantive issues of police control and accountability. Patten envisaged a strong and independent police board linked to a radical system of district policing partnerships, effectively giving local communities a significant role in the running and the application of police functions in their own areas. Some unionists decry this as "Balkanisation" of the police. And it frightens the securocrats.
There are risks, of course, in such an approach. But they are risks which must be taken. Highly centralised policing, on the British (and Irish) model is not the norm outside these islands. Policing with a high level of local input works successfully elsewhere and can be especially suitable for societies with sharply defined differences among people living in close proximity to each other. Mr Mandelson must not allow any dilution of Patten's vision as he presents the Bill in the Commons today. He, the civil servants and the unionist community must let go of the old RUC and take the risk that the natives can behave themselves. They did so in 1922 with the establishment of the Garda Siochana. The likelihood must be they can do the same with the Police Service of Northern Ireland.