WICKLOW TD Stephen Donnelly has announced his resignation from the Social Democrats.

In a statement this lunchtime Donnelly said he was leaving "after a prolonged period of consideration".

"I do so with great sadness, having vested so much together with my parliamentary colleagues, Catherine and Roisin, a small core team and many volunteers across the country, into the establishment of the Social Democrats over the last 20 months.

"It is a fact that some partnerships, in every walk of life, simply don’t work no matter how hard all of the parties to that partnership try to make it succeed."

He added: "For the Social Democrats to achieve its potential as a party of significant influence and scale, despite the many obstacles new parties face, one critical component is that the leadership team must function very well together as a team. In spite of everyone’s best efforts, I have concluded that our partnership did not have that.

"I further believe that this would be the case whether the leadership had continued to be shared or was vested in one person, which was not something I or anyone else had sought."

In its own statement the party said it was "disappointed that he has decided to walk away from the project, we undertook, to establish and build the Party."

"As is the case across the globe the defence of social democratic values is not dependent on one personality or politician - but rather is a collective pursuit."

Its statement said building the party would be "a long term project which requires dedication, hard work, long hours and a major commitment from all involved including our elected representatives. The levels of dedication required for such a major undertaking can be overwhelming for some."

Donnelly had been an active presence for the party in the Dáil chamber, including representing it in Leaders' Questions in July.

A party source insisted this lunchtime that the group would emerge stronger from the difficulty.

But his departure means the combined Social Democrats-Green Party group in the Dáíl no longer has the minimum five members required to ensure automatic speaking rights in the chamber.

Under an hour before the party confirmed his departure, the TD had issued a statement welcoming a government commitment to clamp down on tax loopholes - and made no mention of party affiliation in doing so.