Kyaw Zwar Minn described the apparent seizing of the embassy by the military junta as “a coup d’état in central London”.
Foreign Secretary Dominic Raab condemned Myanmar’s “bullying” that saw the ambassador shut out of the building in Mayfair last night.
The envoy broke with the junta last month when he called for the release of Aung San Suu Kyi, Myanmar’s elected leader who was detained in the wake of the military seizing power on February 1, a move which has sparked weeks of protests.
Troops have violently cracked down on opponents, with security forces reportedly killing 600 civilians.
Photos showed the UK ambassador last night getting out of a black Volvo on Charles Street that bore a large image of Ms Suu Kyi across its rear window.
Kyaw Zwar Minn was also spotted ringing a doorbell as he unsuccessfully tried to enter the embassy, with a small number of police officers standing nearby.
A statement read on his behalf this morning said: “Due to his announcement in March, the ambassador has been recalled by the Myanmar military regime.
“Since then, he has stopped following instruction from the Myanmar foreign ministry and he has been meeting with many diplomatic counterparts and Myanmar community to discuss the current situation in Myanmar, hoping to find a peaceful solution. Due to his stance, the Myanmar embassy in London has been seized by the military attaché yesterday evening. The ambassador has been locked out since then.
“There has been a coup in Myanmar in February and now the same situation in central London.
“This is unacceptable and disrespectful not only to the people of Myanmar but it is also clearly disrespectful to all of democratic society in the UK.”
After finding himself locked out, the ambassador declared it was “a kind of coup, in the middle of London ... you can see that they occupy my building”.
His deputy, Chit Win, has reportedly taken charge of the embassy.
Responding to the extraordinary scenes, Mr Raab tweeted this morning: “We condemn the bullying actions of the Myanmar military regime in London yesterday, and I pay tribute to Kyaw Zwar Minn for his courage.
“The UK continues to call for an end to the coup and the appalling violence, and a swift restoration of democracy.”
Overnight, Myanmar security forces clashed with anti-coup demonstrators in the town of Taze in the North-West, with reports that at least 11 of the protesters were killed and several injured. Troops are said to have fired at protesters who fought back with hunting rifles and firebombs.
Meanwhile, one of Myanmar’s most popular celebrities has been arrested by the military as part of a growing crackdown on artists.
The army ousted Myanmar’s elected government on 1 February, claiming there had been voter fraud in last year’s election.
The independent election commission said there was no evidence to back that up and many people are now regularly being killed at protests over the power grab.
A spokesman for the UK Foreign Office told the BBC that it was “seeking clarification on the current status of the Myanmar ambassador in London, in line with diplomatic protocol”.
Senior General Min Aung Hlaing, leader of the coup, claims pro-democracy demonstrators are trying to “destroy” the country
Ms Suu Kyi had initially been charged with illegally importing six handheld radios and breaching coronavirus protocols.
She has now also been charged under a far more serious official secrets law.
It is estimated that a security force crackdown has claimed the lives of up to 536 people.
There have also been clashes between Myanmar’s military regime and ethnic rebel groups on the country’s border.
A UN special envoy has said that has raised the “possibility of civil war at an unprecedented scale”.