The chairman of the expert group on water charges, Joe O'Toole, has resigned.

The former senator has stepped down following widespread criticism of his comments in favour of water charges.

As recently as this morning, O'Toole had insisted he would remain an impartial and open-minded chair of the expert group, despite publicly disclosing his own support for water charges.

But throughout the morning, opposition TDs had lined up to call for his resignation - and at lunchtime, Fianna Fáil's Barry Cowen told Today FM he was deeply disappointed:

In a statement this evening Joe O'Toole has confirmed his designation - with a sideswipe at Cowen and Fianna Fáil.

Joe O'Toole resigns, with a sideswipe at Fianna Fail pic.twitter.com/BjTJYcQ9hD

— Gavan Reilly (@gavreilly) July 5, 2016

O'Toole said he had been happy to remain in place - but that housing minister Simon Coveney told him Fianna Fáil would not co-operate as long as he stayed.

This would then result in the government being "spancilled" and unable to produce subsequent legislation - something O'Toole was not prepared to countenance.

Earlier in the Dáil Micheal Martin denied Fianna Fáil had been consulted on his appointment as chair of the Commission - though it's understood his party was asked to nominate two of its eight members.

O'Toole's public comments began last week with a radio interview in which he commented that the result of the election had left the government unable to act on the water subject.

He suggested it was up to the expert group to find a way to "add enough sugar to make the medicine go down" - a comment interpreted by many as being supportive of water charges.

The Anti-Austerity Alliance, Sinn Fein and the Social Democrats had called for him to resign altogether, saying the outcome of the work cannot be trusted given the chairman's comments.

Fianna Fail did not call for his resignation, though Barry Cowen said he had no confidence in how his role had been handled to date.

Our political correspondent Gavan Reilly filed this report for Today FM's National Lunchtime News.