If Barack Obama were dreaming up the ideal start to Mitt Romney's first overseas visit as the presumptive Republican nominee, the president might wonder whether his rival could offend the US's historic transatlantic ally.

That would obviously be rejected as impossibly ambitious, so the president might then ask himself whether Romney would fail to remember the name of one of his hosts in London.

Surely a successful businessman would never make such a basic error. So the president would wonder whether Romney would breach convention by saying in public that he met the head of MI6, Britain's overseas intelligence agency.

To the undoubted joy of the White House, Romney stumbled on all those fronts in London on Thursday, the first day of his visit to three of the US's closest allies - Britain, Israel and Poland.

Downing Street, which had gone to great lengths to give Romney the red carpet treatment without breaching strict protocol rules, was astonished when he questioned whether London was capable of running a successful Olympics. In an interview with NBC after his arrival in London, Romney said it was "disconcerting" that the Olympics organizers had encountered difficulties over security. One Whitehall source described Romney's remarks as a "total shocker" that had rendered officials "speechless".

David Cameron wasted no time in delivering a carefully calibrated put down. During a visit to the Olympic Park, the prime minister said Britain was delivering the games in a bustling city. "Of course it's easier if you hold an Olympic Games in the middle of nowhere," the prime minister said in a none too subtle reference to the 2002 Salt Lake City games famously rescued by Romney.

Cameron made clear his irritation when he met Romney later in the day for 45 minutes of talks at No 10. As he emerged from the famous front door – alone to avoid breaching protocol – Romney gave a clue as to why he had stumbled. He reeled off a list of countries he had discussed with Cameron but declined to spell out his thinking in foreign policy on the grounds that only a sitting President should pronounce on overseas soil.

These remarks showed that Romney had absorbed lesson number one of overseas trips that has no doubt been drilled into him by his foreign policy advisers - do not criticize the president when you are out of the US. Sadly for Romney, he forgot an even more important lesson that is so obvious his advisers had probably not bothered to spell it out: try not to offend your host, particularly when he is the leader of your closest sister party in a country that is meant to enjoy a "special relationship" with the US.

The comparisons with Romney's trip to Europe and Obama's visit at almost exactly the same stage in the electoral cycle four years ago are almost too embarrassing to mention. Obama wooed a quarter of a million people in Berlin while Romney was mocked by the British prime minister.

Romney will no doubt be hoping that his faux pas will be remembered as an amusing blip in the Anglo-American special relationship which has undergone a turbulent decade as a left-of-center prime minister embraced a right wing president.

It will not have escaped the attention of Romney that Ed Miliband, a relatively left wing leader of the Labour party, was the most relaxed person of the day when he was referred to as "Mr Leader". Aides said they forgave Romney because US politicians always refer to fellow leaders by their job title.