It has not taken long to extinguish the peace hopes for Northern Ireland which were sparked when the Labour Party won last month's British general election. The point-blank shooting of two policemen in the town of Lurgan on Monday has done more than destroy Tony Blair's offer of talks with the Sinn Fein nationalist movement. The immediate danger comes from the prospect of retaliation by Protestant paramilitaries, who have honoured a cease-fire since October 1994, despite provocation from their opponents. The fear is that the killings will be the flashpoint for full-scale sectarian violence between Protestant and Catholics. It will certainly heighten tension at the most volatile period in the Ulster calendar, the start of the contentious marches by the ultra-Protestant Orange Order. This annual ritual is invariably the scene of pitched street battles, and the prospect of bloody confrontation is now multiplied. Angry and frustrated by their ban from the official conference table, some Catholic and nationalist extremists may feel that recent electoral wins by their political wing, together with renewed popularity in the United States, gives them a licence to resume murder in the province. Whatever claims the political wing of the nationalist Sinn Fein party makes about non-involvement in violence, its leader's statement that the killings 'must act as a huge incentive' to get his party into the talks implies that there is little new thinking in its ranks. Peace efforts will go on, but while there are elements in the IRA with a vested interest in continuing the so-called armed struggle, Northern Ireland's anguish is far from over. It is particularly galling that, with a new British government so open to fresh initiatives and strengthened by a majority large enough to act without the support of the Protestant Ulster Unionists, the men of violence are setting the agenda again. It is they who are the true enemies of their people.