"Morning all," David Cameron jauntily greeted journalists on the scheduled 11am Amtrak train service from Washington to New York. "Hope you are all fans of
The Wire. We are just taking you through Baltimore."

In America, it is the age of the plane rather than the train but the Prime Minister judges that he must be seen to practise what he preaches in the age of austerity. His officials said the train was cheaper, greener and not much slower than flying to New York.

"We're all in this together," is the running joke between Cameron aides and the pack of 30 journalists following him on his first visit to the United States as Prime Minister. The phrase was coined by George Osborne last October as he warned the country of the painful sacrifices everyone would have to make to balance the nation's books.

But it has now become the catchphrase for the austerity drive for Mr Cameron and his officials on foreign trips. White House aides were amazed to learn that the Prime Minister had slummed it on a commercial flight to visit President Barack Obama. Surely, they asked, this is taking Mr Cameron's description of the UK as the "junior partner" in the relationship with the US to ridiculous extremes?

Mr Cameron was probably offered a bump-up to first class by British Airways but that would not have looked very austere and so he flew business class. He managed to stretch out and get "a good sleep" on his seven-hour flight, so it wasn't all that bad. "Very comfortable," was his verdict.

The US media, used to the high life of presidential travel, were also bemused. "I'm afraid we don't have Air Force One. It's a great tragedy," he told a perplexed Diane Sawyer on the ABC network. "We have got a lot of money to save. We've got a very big budget deficit, so we can't go spending money on executive planes, sadly."

His Boeing 777 was delayed for 48 minutes on the Tarmac at Heathrow before take-off, which wouldn't have happened if he had chartered a plane, the long-standing Downing Street practice for long-haul trips. That apart, the austerity drive does not seem to have affected his US visit.

When they sat down to discuss Chancellor Osborne's demand for a 25 per cent budget cut, No 10 officials found they had few easy options. One was the overseas travel budget and the £300,000 typical cost of chartering a plane from BA or Virgin.

Taking a commercial flight to the US this week will save taxpayers between £200,000 and £300,000, according to officials, since taxpayers will not be subsidising the travelling journalists. Another economy measure is that fewer officials will accompany the Prime Minister on his foreign travels.

Some trappings remain. When Mr Cameron landed in Washington, normal VIP treatment resumed. While some of his officials joined reporters in the queue for immigration clearance, Mr Cameron was whisked off to the ornate UK ambassador's residence in Massachussets Avenue. Yesterday he watched Nick Clegg's debut as his stand-in at Prime Minister's Questions from the comfort of the residence.

Tony Blair's plans for the Government to buy a "Blair Force One" – shot down by Chancellor Gordon Brown – are a distant memory. But the age of prime ministerial planes is not entirely over. Downing Street will charter a plane for a visit to India shortly, as 60 businessmen who will accompany him will enable the Government to recoup most of the cost.