Heavy security surrounds the US embassy in Grosvenor Square
It is an iconic focus of protest in Britain - a four-storey modernist concrete fortress, topped with an oversized golden eagle.
For over 40 years those taking issue with American policy abroad have been journeying into the heart of London's exclusive Mayfair - to shout, pray and occasionally try to break into the US embassy in Grosvenor Square.
The building is at the British heart of the US/UK "special relationship".
It is famous for its glamorous four-yearly election night parties and as a compulsory destination for anyone who wants to visit or work in the United States.
Now all is set to change, as the embassy prepares to shut up shop in central London and move to a brand-new building - in somewhat less salubrious surroundings on the south bank of the river Thames.
The reason - the perceived increased danger of terror attacks post 9/11, and concerns that the existing location is just too hard to protect. And London is not alone - several other US embassies worldwide are currently being upgraded or rebuilt on different sites.
The embassy's decision to move has been welcomed by Mayfair's residents, who are frightened of becoming collateral damage in a bomb attack.
They also say the intense security within the square: armed police, huge metal bollards and closed roads have disrupted their daily lives and lowered the value of their multi-million pound homes.
Times have changed, and moving the embassy is a brave and necessary change
Glancing round the prosperous-looking leafy square, quiet in the winter sunshine, it is hard to imagine it as a target of the counter-culture movement in the late 1960s.
Orderly queues of visa seekers snake through the gates, while police in body armour and carrying automatic weapons patrol the pavement. They are quick to interrogate anyone who lingers too long with a camera or notebook.
But former CND member Mick Brown remembers a very different scene - violent protests outside the embassy in March 1968 when thousands of anti-Vietnam war demonstrators clashed with police.
He recalled: "When people got into the square itself they started pulling bits of the fence off and throwing it towards the embassy.
"The police told people that if we had got into the embassy the Americans would have shot us."
Describing the clashes that followed as "a general melee" Mick remembered being hit on the head by a policeman as he bent to rescue a young girl trapped beneath a fallen horse.
He was arrested soon afterwards and charged with assault - something he said "finished his demonstrating career off".
Four decades later, visiting Americans Marjorie and Charles Bosk, from Philadelphia are outside the embassy to admire its architecture - the work of Finnish American modernist Eero Saarinen.
The building is said to clash with its neo-Georgian neighbours
Both were critical of the impending move. "I like my protests in a pretty place," said Charles, sardonically.
But Marjorie said the fact that security concerns have driven her fellow citizens from central London makes her feel "deeply sad".
She added: "We have been displaced from the heart of the city."
There are no regrets from Anthony Lorenz, chairman of the 800-strong St James and Mayfair Residents Association.
Describing fears of bomb attacks and a square "littered with barriers" following the attack on New York's Twin Towers in 2001, he looked forward to the eventual clearance of the square and possible demolition of the building itself, which he described as an "eyesore" in its neo-Georgian surrounds.
Embassy officials acknowledge the embassy's unpopularity with its neighbours was a factor in their decision to move.
In 2003 there was talk of legal action against the US government to seek redress for the falling property prices.
Violent protests outside the embassy in March 1968 resulted in 200 arrests
And last year Grosvenor Square residents took out two-page advertisements in American and British papers accusing the authorities of "moral failure" by exposing them to terror attacks.
At a press conference on Friday US Ambassador Robert Tuttle revealed that plans to shut down and relocate the embassy had been in train since before his appointment to London in 2005.
He described the new embassy's eventual location - a brown-field site in the London borough of Wandsworth currently surrounded by vehicle dealerships and warehouses - as "fabulous".
"We will still be close to the places we need to be - No 10 Downing Street, parliament and Whitehall," he said.
The ambassador made no mention of a dispute with transport authorities over the embassy's long-standing refusal to pay London's congestion charge for its staff.
Officials later confirmed embassy policy would remain unchanged after the move. "We will continue not to pay the charge because we regard it as a local tax, from which diplomats are exempt," said one.
Ambassador Tuttle was speaking at the launch of an international jury which will select the design of the new embassy.
The architectural firm that wins the contest will be an American firm "with the required security clearance", although design teams may include UK partners "with local expertise and international experience."
It is hoped the new, larger, site will be easier to protect, away from potentially litigious neighbours and allow for a building with an iconic status equal to, or exceeding that of, Grosvenor Square.
Muslims pray outside the embassy against the "desecration of the Koran"
Jury member and award-winning British architect Richard Rogers was pragmatic about the move.
"Times have changed, and moving the embassy is a brave and necessary change," he said.
He said the relocation would help to regenerate the area around the new embassy - much as new developments have helped to boost the local economy further down the Thames.
Embassy employees themselves are said to be happy with the plans.
About 1,000 of them - two thirds of them UK citizens - work in a building designed for 750 people. Most "are not fans" of the current building's architecture, said an embassy insider.
But some long-term opponents of American foreign policy see the relocation as bad news for future protests.
Author and activist Tariq Ali, a veteran of the original Grosvenor demonstrations in 1968, recently wrote: "Until now, we could all meet happily in central London.
"A long march to south London is far less enticing."
Other protesters are more optimistic.
Lindsey German of the Stop the War coalition said: "It says something about US policy worldwide that they are moving their embassies.
"But I can assure the US ambassador that we will continue to protest as long as US foreign policy remains unchanged. In fact, I think it's a location that far more ordinary people will able to attend. "