The "special relationship" between Britain and the United States came under pressure this week when a US academic had the cheek to suggest adding salt to tea, sparking a flurry of diplomatic banter.

A "cuppa" tea is a national institution in Britain, about as British as the royal family, pubs and fish and chips, so when American chemist Michelle Francl claimed a pinch of salt was required for the perfect brew, it caused quite a stir.

Keen to repair the damage to relations with its closest ally, the US Embassy in London stepped in.

"We want to ensure the good people of the UK that the unthinkable notion of adding salt to Britain's national drink is not official United States policy. And never will be," the embassy said on X.

"Let us unite in our steeped solidarity and show the world that when it comes to tea, we stand as one."

The tongue-in-cheek post ended by saying the embassy would continue to make tea "the proper way" - by using a microwave.

Britain's Cabinet Office, responsible for overseeing the operation of government, could not resist the fun.

"We appreciate our Special Relationship, however, we must disagree wholeheartedly... Tea can only be made using a kettle," it said.

The quips come 250 years after the Boston Tea Party, when taxes on tea imposed by Britain on its colonies caused a very real split between the two sides, and Americans threw chests of tea into Boston Harbour. War for independence followed.

The "special relationship", a term coined by Winston Churchill, has defined the pair's interactions since World War Two, laying the ground for warm-hearted tea jokes.