A stomach upset or, worse still, full-blown food poisoning is feared by many travelling to far-flung foreign climes every year but the Queen’s top tips for staying in peak health while abroad were revealed to MPs.

When on a trip overseas never eat salads, shellfish or watermelon.

That’s the advice of the monarch, according to Father of the House Sir Peter Tapsell, who once asked a royal courtier how the Queen managed to cope with the demands of often travelling more than 80,000 kilometres a year, and spending time in some of the world’s most inhospitable climates, without falling ill.

“The bedrock of the Queen’s success has been the constitution. Not our constitution but hers because she has always had the most astonishing stamina,” Sir Peter said.

“In 1953, accompanied as always by the indomitable Duke of Edinburgh, she travelled 85,000km. In 1977, the year of her Silver Jubilee, she travelled 90,000km.

“I once asked a courtier how she did it. To which I received the characteristic reply: ‘By not eating salads, shellfish and watermelon while travelling’.” The unusual tip left Prime Minister David Cameron and his Cabinet in fits of laughter.

Sir Peter regaled MPs with his tale in the Commons as the Prime Minister marked the Queen’s Diamond Jubilee by paying tribute to her.

He said she had served the nation with unerring grace, dignity and decency during 60 years of unparalleled change.

The Queen, he said, always knew what to do in a crisis, telling MPs that on one visit to Scotland he shared with the monarch, a local Lord Lieutenant was obstructed by his sword as he tried to get out of his car.

Mr Cameron added: “While embarrassed civic dignitaries cleared their throats, the Queen cut straight through this seemingly insoluble ceremonial problem by walking up to the greeting line, hand outstretched, with the words ‘My Lord Lieutenant appears to be having difficulty in getting out of the car, so I’d better introduce myself. I’m the Queen’.

“That human connection is a hallmark of her reign.”