Mr Bourne was appointed acting leader on Tuesday, prompting the resignation of Mr Richards who had wanted his deputy David Davies to take the post.

Mr Richards had temporarily stood down while he fights an allegation of causing grievous bodily harm to a young woman. He made his resignation permanent when the other Tory Assembly Members rejected his chosen deputy.

Rod Richards to fight criminal charge

"I asked the Tory group to endorse my appointment of David Davies," he said.

"They did not do so. I therefore feel my authority as leader has been undermined and I have no alternative but to resign."

Mr Bourne's application needs three backers from among the other Tory AMs to be valid, but his spokesman claimed he already has the signature of five out of the nine members of the group.

The other four are Mr Bourne himself, David Davies who as the chief whip receives the nomination, Rod Richards and William Graham who is in the USA.

The BBC's Simon Morris: "Nick Bourne takes over a party damaged and traumatised by events of the last six days."

The submission of the nomination triggers the opening of nominations for seven days. If none others are received Mr Bourne will be confrimed as official leader next Wednesday.

It was over the weekend that Mr Richards "stepped aside" from the leadership following allegations of assault made against him by a 22-year-old woman.

Assault 'fabrication'

Married with three children, he is charged with causing grievous bodily harm to Cassandra Melvin on 27 July, at Kew in west London.

But he described the assault charge as a "complete fabrication", and vowed to fight it.

The BBC's Caroline Evans looks back at the highs and lows of Rod Richard's colouful career

Mr Bourne's appointment was made at a Conservative party meeting in Cardiff, just hours before Mr Richards' resignation.

Mr Richards spent only 10 minutes at the gathering, emerging to say he had once again asked AMs to back Mr Davies as deputy leader. He had, he said, left the decision with them.