Northern Irish politician Ian Paisley has claimed he told Tony Blair he was a fool when the former Prime Minister informed him he was converting to Catholicism.

The founder of the Free ­Presbyterian Church and long-time critic of the papacy in Rome said Mr Blair revealed his decision to him as they left a private meeting together in 2007.

Speaking in a wide-ranging interview, Dr Paisley said: "As we were walking down the stairs he stopped, he looked back at me and he said 'Ian, there is something I need to tell you'.

"'When the hands of that clock', and he pointed to a big clock that was on the wall, 'When the hands of that clock, when they come to eight o'clock I will be a Roman Catholic'.

"And he said 'I didn't want you to leave without telling you, I'd rather tell you myself'.

"And I said 'You are a fool' and I walked on."

In a new BBC documentary reflecting on his career in politics, Dr Paisley's wife also described how his decision to share power with his long-time foes Sinn Fein led to him losing one of his closest friendships.

Emminent QC and former MP Desmond Boal, who founded the Democratic Unionist Party (DUP) along with Dr Paisley in 1971, would have nothing further to do with him after the historic deal with republicans in 2007, Baroness Eileen Paisley said.

Prior to that the pair had forged a strong allegiance through the decades, with Mr Boal often acting as the DUP's main legal adviser.