By Nyta Mann BBC News Online political correspondent

Tony Blair is entirely accustomed to travelling some way ahead of those he seeks to coax, convert or pressurise towards his own point of view.

It is a defining motif of his political career, with Mr Blair frequently adopting policy positions of extreme discomfort for his own party.

Whenever he has looked like disappearing too far over the horizon, close confidants have warned him to watch he doesn't get too far in front of what those still to catch up are prepared to accept.

But never has the prime minister been quite so distant, almost to the point of isolation, as he appears now - both at home and abroad.

Europe or the US?

US President George Bush appears more determined by the day to go to war with Iraq. Equally, there is no evidence of any let-up in the prime minister's determination to stick "shoulder to shoulder" with the US.

At the same time, the gulf between Europe and America has widened.

Donald Rumsfeld: Attacked "old Europe"

Mr Blair now faces the prospect of having to make the choice he hoped would not arise: Europe or the US?

He is far from the first prime minister to have to deal with the balancing act of maintaining influence in America while seeking to play a central role in Europe.

It was Winston Churchill who, making clear which way he would go if forced to decide between the US and Europe, said: "Each time we must choose between Europe and the open sea, we shall always choose the open sea."

He was talking to the French leader Charles De Gaulle, and went on: "Each time I must choose between you and Roosevelt, I shall always choose Roosevelt."

Franco-German doubts

This wartime exchange was later cited by De Gaulle to justify his later blocking of Britain from joining the Common Market. It betrayed the impossibility of Britain ever being truly committed to Europe, he maintained.

Decades on, it is all very well for US Secretary of State Donald Rumsfeld to dismiss deep-felt Franco-German reservations on war with Iraq as an irrelevance of "old Europe".

But France and Germany remain the motor of the European Union, of which the UK is a member - an aspirant leading one at that, according to Mr Blair himself.

What hope of that now if he ends up caught between a US gung-ho for war and the rest of Europe either straightforwardly and openly opposed or quietly against military action against Iraq?

Lonely on the home front

The prime minister's position is no less lonely at home.

There is deep scepticism within his cabinet, alarm on his back benches and unhappiness in the rank and file - and not just over the war.

But unlike most previous occasions when he has found himself out of step with any or all of the above, Mr Blair has no recourse to public opinion, which has remained stubbornly unconvinced by the case for war.

In their journey from opposition to office, Mr Blair and his closest political allies have always stressed, to themselves and to others, that central to their success is continual momentum, never resting, always pushing ahead.

"No matter the discomfort, lead and others will follow," has been the approach.

It is, of course, just about inevitable that at some point he will simply travel too great a distance ahead of too many of those who have thus far journeyed with him - sometimes reluctantly, often with misgivings.

Whether the looming war with Iraq is that point, nobody can know.

What is already certain, however, is that Mr Blair has never been quite so precariously ahead of those he expects to back him as he is now.