Following a lengthy stint in the banking inquiry's witness box, former taoiseach Bertie Ahern has re-emerged to vent his spleen at the Mahon tribunal, which led to his resignation.

The former leader of Fianna Fáil gave an hour-long interview to Miriam O'Callaghan on RTÉ Radio One on Sunday morning that will have prompted groans across the political spectrum.

Mr Ahern even gave something of an endorsement to the current administration, saying the Fine Gael-Labour coalition was "doing a good job" building on work done by previous Fianna Fáil-led governments.

And there was some rare good news for Minister for the Environment Alan Kelly: Mr Ahern has paid his water bill.

“Yeah, I’ve no problem with the water charges,” he said.

The Mahon tribunal rejected Mr Ahern’s evidence in relation to his personal finances as mostly “untrue” and found that, contrary to his sworn evidence, there were no dig-outs in 1993 and 1994 .

While claiming on Sunday he wanted to let bygones be bygones with tribunal chairman Justice Alan Mahon, Mr Ahern’s tone indicated otherwise.

“I don’t hold any grudges to him or his legal team. I want to move on with my life, but they’re wrong, they were wrong then, they’re wrong now and they’ll be wrong ’til the day I die.”

Leaving Fianna Fáil after 41 years of membership was a “terrible” moment, he said.

He declined to say if he would re-enter the fold if asked by party leader Micheál Martin. Mr Martin was not available for comment.

However, maverick TD John McGuinness said he was sure Mr Ahern would be welcomed back. The Kilkenny deputy said Mr Ahern had “adequately and competently” explained himself.

“We have to learn from the past and get on. He’s faced his accusers,” Mr McGuinness said. “Many other members have left and come back so quite honestly I wouldn’t have any difficulty with it. If someone said to me in the morning he’s coming back I’d say, so what?”