"Many people will share the profound sympathy I feel, that your cabinet career has come to an end in this way."

He added these were "clearly such difficult times for you and for Chris (Mrs Davies)".

New Welsh secretary Alun Michael

"I was very proud and delighted to be asked by the prime minister to be Secretary of State for Wales, but for it to come in these circumstances is a great sadness.

"This is a tremendous blow for Ron Davies and his family.

"My priority is to look at the work that has been done by Ron and his colleagues, and to look at the immediate challenges and decisions that face us to make sure that the Welsh Office does everything possible to position Wales to take advantage of the opportunities that are there for us over the next year or two."

Welsh Office Minister Peter Hain

"We are all astounded by Ron Davies' resignation and our sympathies go out to him and his family.

"Ron is a good friend and political colleague who did more than anyone else to secure a new democratic future for Wales. His resignation is a personal and political tragedy."

Dafydd Wigley, president of Plaid Cymru

"Ron Davies resignation was an absolute shock to us. I have no doubt it was very serious issue for him to resign.

"This is a personal tragedy for Ron Davies and his family and a tragedy for Wales because he had played a very important role indeed in developing a national assembly for Wales and leading the campaign for the referendum.

"There is no indication he is standing down as MP for Caerphilly and there's no reason he should not stand as a candidate for the national assembly."

Conservative constitutional spokesman Dr Liam Fox

"I thinks it's always sad when someone's private life swamps their professional career.

"He's obviously come to a decision that's impossible for him to continue in the cabinet ... we can't make a judgement since we are not aware of what those facts were.

"I'm sure that's a matter for him and his constituency party to come to an agreement about. I've not heard anyone who said he was incapable of doing his job as a member of parliament.

"He said that he had a lapse of judgement that meant he could not continue in the cabinet I think that's a very different matter."

Ann Clwyd, Labour MP for Cynon Valley

"Ron did a very good job in securing the vote and then the referendum for the assembly, and he has been a very vigorous voice for the people of Wales.

"I am extremely sorry that this should have happened."

Llew Smith, Labour MP for Blaenau Gwent.

"My differences with him are political.

"Without knowing anything really about what has happened to Ron, I think it's sad.

" No one would wish that on anyone, no matter what their political beliefs."