Brendan Duddy, who played a secret role in the 1970s, 1980s and 1990s, is now an independent member of the Policing Board.

Writing exclusively in the Telegraph today, Mr Duddy acknowledged that the DUP had a right to demand clarity from Sinn Fein - but he also insisted that Gerry Adams and Martin McGuinness had delivered it.

In a candid article, Mr Duddy said: "Nice people have chosen to believe their own myths that it was only a hard core of Sinn Fein activists who would not accept a policing service. This was never true and that is why the Sinn Fein meeting in Dublin offers, for the first time in my lifetime, real hope for a better Ireland, north and south."

He continued: "It would be unforgivable not to grasp this opportunity."

The comments came as Ian Paisley and Gerry Adams were each fighting today to hold the nerves of their parties in the aftermath of Tony Blair's direct intervention into stuttering negotiations.

After Mr Blair threatened to call off next March's Assembly election - putting the prospects for devolution into deep freeze - Mr Adams has called Sinn Fein's leadership team to a key strategy meeting next week.

And the DUP has called on its members to watch their words while the Government grapples with the hurdle of policing.

Mr Blair wants Sinn Fein to go ahead with a key party conference on support for the PSNI later this month - and he wants the DUP to give an undertaking that they will agree to the transfer of justice powers to the Assembly next year.

The Government says Mr Blair's intervention will be successful, but neither Sinn Fein nor the DUP has so far changed their public position.