The decision to build a new embassy was made during George W. Bush's presidency.
President Donald Trump said he has called off a planned ceremonial visit to Britain because he didn't want to be associated with what he called a bad real estate deal in which the U.S. Embassy is being relocated from central London to "an off location".
"Bad deal", Trump said, adding "wanted me to cut ribbon - NO!"
British opposition politicians said Trump was not welcome in the U.K. Former opposition Labour party leader leader Ed Miliband tweeted to Trump that the reason he cancelled was really "because nobody wanted you to come".
Rex Tillerson, the USA secretary of state, is expected to attend the embassy's opening instead. It's possible that plans for "mass protests, those optics he didn't like the look of".
Details of the official state visit by Trump, planned for later this year, are still being ironed out.
Protesters outside the previous embassy with its distinctive eagle
Khan said Trump's visit next month "would without doubt have been met by mass peaceful protests".
United States president Donald Trump has confirmed he won't be coming to Britain to open the new USA embassy in February. He said it was due to concerns about the embassy's move from the elite Mayfair district to a less fashionable area of London.
Trump has also been offered a full-blown state visit to Britain but no date has been set, amid jitters over protests.
The US Government has attempted to purchase the building before, but the previous Duke reportedly said he would only sell it if the (considerable) land confiscated from his family during the War of Independence was returned. The British Prime Minister told Trump that to do so was "wrong", to which he responded by telling her to focus on the UK's "destructive radical Islamic terrorism", rather than him.
Mass protests would have likely greeted Trump, with Labour Party leader Jeremy Corbyn telling followers they should send the U.S. president a "clear message" by demonstrating again him.
Downing Street said no date has been confirmed for any visit by Mr Trump and that the opening of the U.S. embassy "is a matter for the US".
Some British lawmakers questioned whether Trump would be welcome after he re-tweeted videos from a far-right British group and criticized London Mayor Sadiq Khan following a terror attack a year ago.