David McKittrick: Will the fundamentalist Paisley prevail over the moderates within his ranks?

The man everyone will be watching, as vital talks on the Northern Ireland peace process take place at Leeds Castle in Kent today and tomorrow, is the Democratic Unionist leader, the Rev Ian Paisley.

The success or failure of the negotiations, which London and Dublin hope will re-establish power-sharing government in Belfast, may well rest on the volatile 78-year-old Protestant patriarch.

Both his health and his inclination to compromise are in question. He travelled to Kent from Belfast by ferry and car, his doctor having advised him against flying.

Since the DUP's striking electoral successes have made it Unionism's major political voice, the key issue will be whether it can contemplate a historic new deal with Sinn Fein.

Both the DUP and the republicans have hinted that a deal is not impossible, but it will take sizeable concessions from both sides. Huge question marks remain; the first being whether the IRA is willing to move decisively away from paramilitarism. The second is whether, in this event, Mr Paisley will agree to share power with Sinn Fein.

Just as republicanism encompasses both militants and moderates, so the DUP now contains different tendencies.

Much will therefore turn on the power balances within the DUP, and whether republicans will offer the kind of deal to engage the party.

Mr Paisley is not the overwhelming figure he once was, but within his own party he almost certainly retains the power to veto any movement towards a deal. He produced an old-style Paisley detonation recently when questioned about the state of his health.

He reacted in a bellicose manner, with an eruption against "Romanist" journalists. This has raised worries that he continues to view the Northern Ireland problem as one which is primarily religious rather than political.

Since he does not regard the Catholic Church as Christian, one fear is that he may not be able to contemplate any reconciliation with Catholics and nationalists.

Such fundamentalism sits side by side with the new pragmatism. Over the summer those involved in the extensive preparatory contacts leading up to the Leeds Castle encounter have been impressed by the DUP's engagement. The party has noticeably refrained from making absolutely impossible demands.

Republicans probably stand ready to make significant concessions. But they will be seeking guarantees that the DUP will respond with concessions of its own.

Like everyone else they will be watching warily to judge whether the new-style DUP is led by a newly flexible Ian Paisley, or the familiar old fundamentalist.