ITis always a convivial night in late January when the festive season is fading in the memory and politicians and journalists come together for an evening of good cheer.

Jamie McGrigor, Tory MSP, always gets his guitar out and sings a couple of satirical ditties - this year the first minister's kilt was the subject of one, while anotherwas a joke at the expense of the Daily Telegraph - and sometimes guests will drink more than is good for them, such as the journalist who slipped in the toilet and broke his nose one year.

But this year it happened to a politician, who was being pursued by a tabloid newspaper over his love-life, and the consequences were different.

Yesterday, David Davidson, 62, resigned as his party's front bench spokesman on health.

As party spokesman he was much given to comments on alcohol abuse, personal responsibility, sexual health and the merits of the family.

But while his wife was at home in Stonehaven he was spending nights with anotherwoman, an MSP from a rival party.

Rumours of this abounded for months and when he fell over after a drinks reception and broke his leg, a team from the News Of The World was watching. On Sunday, the newspaper said that he and Christine Grahame, the SNP MSP, had spent the night at each other's homes in Edinburgh on three occasions last week.

Mr Davidson, who is married with five children, said that he and Ms Grahame were close friends but were not having an affair and said they had slept in separate rooms.

He could have tried to brazen it out, as the party made clear on Sunday that it was treating revelations as private and personal matters. But the combined effect of rhetoric, conduct and press revelation was to wreck his credibility.

A phone call to David McLetchie, his Holyrood leader, followed the inevitable exchange of letters.

Thursday's contributions alone tell the story. During the debate on the executive's sexual health strategy he said: " I am particularly pleased to hear his (Andy Kerr's) comments about the encouragement of personal responsibility for one's own health and the need to have respect for the care and health of those for whom one has a responsibility.

"I appreciate the comments that he made about the family.

I also appreciate the assurance that the minister gave that the morning-after pill will not be distributed like sweeties in a school."

This brought an angry intervention from the minister.

Later, just before leaving for the reception, he said in a debate about fertility services:

"In case anybody thinks I am the token male in the debate, I should say that I have done my bit for family raising.

"I had five children - with my wife, I might add - and I still have some responsibility there."

Later still, he left the reception to go on radio to talk about the need for emotional maturity and the avoidance of peer pressures to lose control through drink or drugs. Again he pointed out he was a "father of five" who had been able to impart "basic values".

When he was fell over outside the reception he insisted on calling Ms Grahame, the SNP's shadow communities minister, to come to his aid, against advice.

Yesterday, Ms Grahame was at her desk as normal and was continuing to refuse to comment.

Now the Tories have promoted their deputy health spokesman, Nanette Milne.

She will not relish the spotlight of the front bench the way Mr Davidson did, and has at times looked uneasy under the cut and thrust of questioning.

She brings to bear a medical career dating back to 1965 with spells in both anaesthetics and cancer research.

She also has considerable political experience at both council and party levels.

THE CORRESPONDENCE

David Davidson's letter to David McLetchie

Dear David, Following our telephone conversation earlier today and my visit to the outpatient clinic, I have decided that it would be best if I stood down from my role as health spokesman for the party.

The doctors have advised me that I face a month in plaster, subject to further consultant approval, before I can start to put any weight on my leg. In addition, the events of the last 48 hours, not least the allegations and insinuations in the newspapers, have led me to the decision that it is in the best interests of my family, my health and of the party that I take this action.

I will, of course, continue to play my part as a member of the Scottish Conservative team in the Scottish Parliament as we hold to account the failing Labour/Liberal Democrat executive.

I thank you for all your support.

Yours ever, David Davidson

Mr McLetchie's reply

Dear David, Thank you for your letter tendering your resignation as our health spokesman. I fully understand the reasons for your decision and wish you a full and speedy recovery.

I would also like to thank you for the substantial contribution you have made as our health spokesman in this parliament in highlighting the Conservative alternative to the failed policies of the Scottish executive.

Your remain a valued colleague and I look forward to working with you in the years to come.

Kind regards.

Yours sincerely, David