Pregnant Samantha Cameron 'too knackered' to fly with PM on first official visit to U.S.By James Chapman

Samantha Cameron will not accompany her husband on his historic first trip to the United States as Prime Minister.

Most airlines allow pregnant women to fly up to and including the 36th week, provided the pregnancy has been straightforward.

Mrs Cameron's baby is understood to be due in early September, meaning she could still travel if she wished.

But she pulled out of a trip last month to the G8 and G20 summits in Canada, citing exhaustion, and has apparently baulked at the prospect of another long flight.

She will also miss a trip by the Prime Minister to India to promote a new 'special relationship' with Britain later this month.

'Samantha Cameron was very keen to come to India, but she won't be coming as she is expecting a baby in September,' said one British diplomat.

'The Camerons are very thrilled at the news and don't want to take any chances with the baby on the way.'

The couple tried for another child after the death of their six-year-old son Ivan, who suffered from cerebral palsy and epilepsy, last year.

Even if Samantha was in a condition to to travel, she may not have been accompanying her husband anyway.

The Prime Minister - in a bid to show that everyone is tightening their belts as part of the Government's austerity drive - has chosen to take commercial flights to America.

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Mr Cameron will have three hours in the White House and plenty of face-to-face time with the President - in stark contrast to visits by former PM Gordon Brown, which were dogged by rumours of the Labour leader being snubbed by Mr Obama.

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Of course Mr Cameron will have plenty to talk about with Mr Obama, and not all of it will be pleasant.

There is the continuing BP crisis in the Gulf of Mexico, which Mr Cameron has been keen to stay clear of but will be uppermost in Mr Obama's mind.

Then there is the release of Lockerbie bomber Abdelbaset Al Megrahi, who was freed last summer on compassionate grounds because he was supposedly dying of cancer.

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Washington was unhappy at the release of a man who had been found guilty of killing 190 American citizens - especially when it was suggested that BP lobbied the British Government for his freedom in return for an oil deal in Libya.

But there is evidence that Mr Cameron and Mr Obama are trying to keep the ofton-mentioned 'special relationship' between the teo countries.

Last month in Canada, Mr Obama even gave Mr Cameron a lift in his helicopter from the G8 to the G20 summit.

It doesn't get much friendlier than that.

Topics of conversation: Mr Obama will want to talk with Mr Cameron about the continuing BP crisis and the early release of terrorist Abdelbaset Al Megrahi.