Tony Blair: World's cares on his shoulders, Peter Cook on his bedside table

As Tony Blair nursed his cold in the back of an armoured Jaguar on the way to his flight home after addressing the Welsh Labour conference last Friday, he was passed a note. The Rhondda Constituency Labour Party, deep in the traditionally socialist heartland of South Wales, had concluded after a long discussion that it was confident that whatever decisions he took, they would be the right ones.

It was a heartening message less than 48 hours after the Blair government had suffered its worst rebellion when 122 Labour MPs voted against his strategy. But then Mr Blair has never been overly diverted from his own judgement by the views of the party he leads.

That isn't to say that he is particularly belligerent about it even in private. He will repeatedly tell anyone who asks that he has made a "judgement call" about Iraq and that he respects and understands the views of those, including some of his friends, who don't. He is also fond of pointing out that while some of his opponents are long-time Blair admirers, some of his supporters are usually critics, among them the MPs Ann Clwyd, a long-time campaigner against Saddam Hussein and the fiercely independent-minded Andrew McKinley. He rarely, if ever, comes on in private as a warmonger, pointing out to colleagues that while everyone remembers he persuaded to Bill Clinton to threaten a ground invasion against Slobodan Milosevic during the Kosovo war they tend to forget that it was also he who earlier advocated giving the Serbian President an extra two months to see sense before the negotiations at Rambouillet broke down and the bombing started.

He insists he was concerned about Iraqi weapons of mass destruction and told George Bush so as long ago as February 2001, long before 11 September. And he still thinks that if from January – in the wake of Iraq's 12,000-word declaration denying any possession of weapons of mass destruction – the international community had acted in unison, disarmament could have happened without war.

So Mr Blair isn't losing much sleep about the turbulence in his party, a turbulence which could become much more intense if he follows President Bush into Iraq without the sanction of a new UN resolution. The sheer volume of diplomatic contacts, compounded by the number of time zones they daily traverse is, of course, costing him sleep. But although he is not a consistent four-to-five hours a night Prime Minister, as Margaret Thatcher was, he can do without much sleep for long periods. As his premiership faces its most decisive test, what frequently does cost him rest is baby Leo, who rarely sleeps through the night, and to whom he has somehow managed, amid everything, to remain a closely bonded parent.

So how does he relax? He is has become something close to a fitness fanatic, working out or playing tennis nearly every day. He famously plays the guitar. And his reading isn't confined to the reams of intelligence reports and Cabinet papers he gets each day. Most recently he has been reading the new book of Peter Cook scripts, Tragically I was a Single Twin, a gift from an old school friend. Not surprisingly perhaps, he enjoyed Cook's brilliant 1962 take-off of Harold Macmillan, in which the old showman describes his discussions with Jack Kennedy of Britain's role as a global "honest broker". "I agreed with him when he said we had never been more honest. He agreed with me when I chaffed him and said we had never been broker."

That Mr Blair is facing his most perilous period as Prime Minister isn't in doubt. And his critics underestimate him if they assume he shows any sign of cracking under the strain. If anything, he is more self-confident, reflected, some say in a more robust attitude to his frictional, if pivotal, relationship with the Chancellor, Gordon Brown. And he has not let Iraq distract him from pressing domestic issues, asylum and public service reform among them. But he tells friends he is always at his best and most focused when he is dealing with a single issue of prime importance.

You only have to look at those astonishingly youthful television pictures of him before the 1997 election to see the strains of office have taken their toll. Last week he said he had to make difficult decisions before – not least over Kosovo or Afghanistan – and he was simply asking people to trust him again this time. That is not enough for his critics on Iraq, and it leaves open the question of how far he has been pushed to this by circumstances and a US President. But what is not in doubt is his physical and mental shape. This is not a man about to lose his nerve.