Irish Taoiseach Brian Cowen speaking to the media with Northern Ireland's Deputy First Minister Martin McGuiness and former First Minister Ian PaisleyAFP/Getty Images

Irish Taoiseach (Prime Minister) Brian Cowen and Sinn Fein leader Martin McGuinness came very close to blows and a stand up fight during negotiations on Northern Ireland.

The revelation comes in the new book by former Prime Minister Bertie Ahern, which is serialized in the Sunday Times Irish edition.

Ahern reveals McGuinness and Cowen lost their cool in talks in early 2004 over Ahern’s allegations that Gerry Adams was in the IRA. During the discussions Cowen, now taoiseach but then minister for foreign affairs, became incensed by the insulting tone he felt Sinn Fein were using.

“Eventually he stood up and banged his fist on the table. ‘You will not speak to the taoiseach of our country in that way!’ he roared. McGuinness jumped up and the two of them stood eyeball to eyeball, neither saying anything.”

Ahern also reveals that while he spoke to Gerry Adams, the Sinn Fein leader, almost every week during his 11 years as taoiseach, he felt he hardly knew him at the end. Adams was “hard work,” and “sometimes he could be cross and difficult.” Ahern writes.

However, McGuinness was easier to get along with.

“While Adams could be narky, Martin McGuinness was more personable. He would ask about my family and talk about sport or fishing. He was more friendly and approachable. He was also more emotional in talks. Gerry would usually be fairly bland about things, so you could never be sure if he was happy or annoyed. If Martin was angry, you knew it.”

Ahern is also highly critical of former Northern Ireland Secretary Peter Mandelson who he says “slowed the peace process.”

“We never really hit it off with Mandelson. Talks with him were always heavy weather. Partly it was his manner, which was a bit standoffish “I think he liked being up at Hillsborough Castle, where he could play the ‘viceroy.’ We were always doubtful about him. Nobody thought he compared to Mo. Mowlam”

“There was no doubting his intelligence, or even his charm when he decided to turn it on. But he had unfettered access to Tony Blair [the then prime minister], which made it difficult to go over his head,” the former taoiseach says. “When he went in January 2001, we were glad to see the back of him.”