Mr Peter Mandelson flies into Belfast this morning for a preliminary round of meetings with officials, security advisers and party leaders, having vowed to "work night and day" to achieve a deal acceptable to all sides in Northern Ireland.
The newly appointed Secretary of State will be accompanied by the departing Dr Mo Mowlam, who last night insisted she had not been "forced out" of her Stormont job under continuing unionist pressure.
Dr Mowlam's departure and her replacement by Mr Mandelson had been privately predicted by senior Ulster Unionists over the past fortnight.
Mr Mandelson's cabinet comeback, in a wider-than-expected reshuffle, marks a remarkable recovery barely 10 months after he was forced to resign as Trade Secretary after revelations about his controversial home-loan. His speedy return to the political front line was being seen last night as clear evidence of Mr Tony Blair's continuing reliance on him in the context of the New Labour project, and of the prime minister's continued dedication to the peace process.
Speaking alongside Dr Mowlam on the steps of 10 Downing Street, Mr Mandelson said he hoped his appointment would "demonstrate the government's absolute unwavering commitment to finding peace and reaching a deal in Northern Ireland.
There is nothing more important than finding a deal that is acceptable to everyone. I shall work night and day to do everything I can to achieve that."
Speaking on Channel Four News last night, Dr Mowlam - who becomes the so-called "cabinet enforcer", responsible for cross-departmental co-ordination of government policies - maintained she was happy with her new job, and "pleased that it's Peter Mandelson who took over from me".
Dr Mowlam said she had not been forced out by the unionists, adding that demands for her resignation had come at various times from both sides. The departures of Lord Robertson and Mr Frank Dobson for other jobs, and the surprise resignation of Dr Jack Cunningham, had given Mr Blair the chance of a wider reshuffle "and he took it".
Dr Mowlam said Mr Mandelson had the necessary "communication and tactical skills" and she was "very glad he's taken over".
However, Dr Mowlam had seemed and sounded regretful earlier in the day as it became clear she was to give up the portfolio she had carried for five years in opposition and government.
Clearly feeling the emotion of the occasion, Dr Mowlam said: "I am sad obviously to be leaving the job. I have got a lot of good friends now and it is a beautiful place to work. There's never an easy time to go. Now is clearly not an easy time, but everybody has to go at some time."
Mr David Trimble, the Ulster Unionist leader and First Minister designate, welcomed Mr Mandelson's appointment but denied it was a personal victory for him. Mr Trimble first suggested Mr Mandelson for the Stormont post when calling for Dr Mowlam's removal at a press briefing in London in the early summer.
Yesterday, however, Mr Trimble insisted: "Some of the things I have seen in the press about the relationship with the Secretary of State have been very wide of the mark. Mo Mowlam and I were always able to do business." He added: "We wish her all the best for the future."
Mr Trimble, who will be among the first to meet the new Secretary of State, doubted if Mr Mandelson's arrival would mark any great shift in British policy in Northern Ireland. "It's a government and, unlike some parties, it remains coherent," he said.
The new Northern Secretary and Dr Mowlam will meet a Sinn Fein delegation led by its chief negotiator, Mr Martin McGuinness, today. Mr Mandelson will also have an early meeting with the Minister for Foreign Affairs, Mr Andrews, as the Mitchell review of the Belfast Agreement enters its make-or-break phase.
The other big priority for the new Northern Secretary will be to carry forward the consultation exercise on the Patten proposals on the future of policing.