The new embassy on the South Bank is a veritable fortress set back at least 30 metres from surrounding buildings - mostly newly-erected high-rise residential blocks - and incorporates living quarters for the US Marines permanently stationed inside.
The embassy's new cube-shaped building is designed by American architect KieranTimberlake and will be open for business on Tuesday.
Writing in London's Evening Standard newspaper, Johnson said the move from central London to Nine Elms, next to Battersea, was forced by security concerns after 11 September.
"Vauxhall is a vibrant and important part of London and home to many businesses", May's spokesman Max Blain told reporters yesterday.
But a full-blown state visit replete with golden carriages and pomp has been deferred amid the threat of huge anti-Trump protests.
May's spokesman told reporters Trump was welcome in London and that the invitation to visit had been accepted, although no date agreed.
Trump asserted late Thursday on Twitter that he "canceled" his trip to the United Kingdom next month because he didn't like the deal under which the embassy was moved.
Bannon to Testify Before House Intelligence Committee in Russia Probe
US President Donald Trump walks to Marine One before leaving the White House on January 5, 2018. Trump said "we'll see what happens" when asked if he'd provide an interview to Mueller's team.
The president, however, had become fed up with all the criticism and considered it an affront not only to his administration, but to his country, a White House official said yesterday. She suggested a formal visit could still, but offered no details.
Relations between the USA and its closest ally have been tested repeatedly since Trump took office nearly a year ago.
His decision not to come was welcomed by critics outraged by the USA travel ban on Muslim-majority countries, and more recently, Trump's decision to re-tweet anti-Muslim videos posted by a British far-right organisation.
Many British politicians have voiced their opposition to Trump being granted a state visit, and say the invite should be recalled.
Trump's cancellation was met with humour on social media, with parodies of the president's tweet trending on Twitter.
The exchange prompted further calls to dump the visit. "Many Londoners have made it clear that Donald Trump is not welcome here while he is pursuing such a divisive agenda", Khan said on Friday. He said the opening of the embassy was a matter for the U.S. government.
A Number 10 source said: "Boris expresses himself in his own inimitable way, but we agree that any risk to the crucial US-UK relationship is not in our country's best interests".
"We will not allow US-UK relations to be endangered by some puffed-up, pompous popinjay in City Hall", Johnson tweeted.