JACK McConnell will be

formally installed as the third first minister of Scotland next week, having yesterday attempted to thwart a potential scandal by admitting he had an affair seven years ago.

In an extraordinary day for Scottish politics, Mr McConnell first made a startling public confession that he had betrayed his wife and family.

He then pleaded with the media to respect his privacy from now on.

Six hours later, he emerged as Labour's only candidate for the party leadership.

Mr McConnell's frank confession was met with an equally frank statement by his wife, Bridget. ''Jack betrayed my trust,'' she said.

His unstoppable progress leaves Labour without a contest for the succession to Henry McLeish, despite Mr McCon-nell's own calls for a Scotland-wide public debate about the issues.

Instead of the month of hustings, Labour MSPs expect to be called to a meeting with party executive members on Saturday, where they will anoint their new leader in a so-called ''affirmative ballot''. He seems certain to be first minister on Wednesday.

John McAllion, the left-winger who had hoped to make at least a token challenge for the leadership, was the only other MSP to receive a nomination from among Labour's 55-strong Holyrood group. Lesley Quinn, party general secretary, would not identify the individual who nominated him, but said it was not Mr McAllion himself. He needed seven nomiations to stand. Mr McConnell received 33 nominations - virtually all the Labour back benchers plus some junior ministers.

By the middle of next week, the formalities will be over, leaving the 41-year-old former maths teacher from Arran, known as Jack the Lad because of his reputation for nerve and risk-taking, leading the government of


But as the furore over Mr McLeish's wrongly claimed expenses died down, several tabloid newspapers were last night in hot pursuit of more details of Mr McConnell's past behaviour. The woman involved in his former liaison remained silent.

Mr McConnell indicated she had been made aware of his intention to talk of their affair, but it appeared he had not necessarily received her agreement.

At a tense and tightly controlled news conference called to ''clear the air'', a plainly uncomfortable Mr McConnell, sitting with his wife, parried questions about whether he would resign if there were further revelations about his personal life.

He had summoned journalists to confess his previous ''mistake'' in the hope that the tabloids would leave him in peace.

''I want to be clear about one aspect of my past,'' he said. ''It has been an open secret for seven years. It caused significant hurt to a number of people and I regret that very much to this day.''

He then confessed to lying publicly and privately about his behaviour and added: ''I let everybody down. I love my family very much and I have always tried to keep our private life private.''

A dignified but unsmiling Mrs McConnell, director of cultural and leisure services with Glasgow City Council, said she supported his bid to become first minister, and told reporters: ''Jack betrayed my trust seven years ago by having an affair. It goes without saying he hurt everyone involved. The resolution of this crisis in our marriage remains a private issue.''

As observers debated the wisdom of Mr McConnell's initiative in talking in public about his personal conduct, his opponents lined up to attack Labour for the manner of his victory.

Tommy Sheridan, Scottish Socialist leader, denounced the lack of opposition to the education minister and MSP for Motherwell and Wishaw as a farce. ''The Labour Party is now resembling the Vatican: leaders emerge with a puff of smoke, not a vote,'' he complained, challenging the first minister-designate to a public debate about the ''real issues''.

Roseanna Cunningham, the SNP's deputy leader, took up the theme, saying the lack of contest was ''utterly pathetic and deeply damaging for democracy'' in Scotland.

''It is clear that the Labour party has not learned their lessons over the McLeish debacle. Henry McLeish was foisted upon the people of Scotland as first minister simply because he had the support of certain senior Westminster members.

''Now Jack McConnell will be forced on the people of Scotland simply because Labour has already scraped the barrel and is unable to come up with a candidate to oppose him,'' she said.

The Tories, who helped overthrow Mr McLeish, were less scathing. David McLetchie, party leader, congratulated Mr McConnell, but warned: ''Jack McConnell may have been given a walkover by his Labour colleagues, but he can expect no such leniency from the Scottish Conservative Party.

''I look forward to tackling Mr McConnell in the chamber over his party's dismal failure on the issues that really matter to the people of Scotland.

''The record of the Labour-LibDem Scottish executive is truly woeful. It will take more than a change of leader to mask this simple truth.''

Mr McLetchie offered no comment on Mr McConnell's confession, leaving Annabel Goldie, deputy leader, to remark: ''It is not for the Conservative Party to judge Mr McConnell on the statement he made today, which concerned matters of a private nature.

''The public has to make its own judgment on such matters. What does matter is that Mr McConnell is shown to be a man of integrity, honesty, and propriety.''