Kyaw Zwar Minn was denied entry to the building on Charles Street in Mayfair on Wednesday night.
The Foreign Secretary on Thursday paid tribute to the "courage" of diplomat Kyaw Zwar Minn, who reportedly spent the night in his vehicle having been locked out the evening before.
The BBC reported last month that Kyaw Zwar Minn had been recalled by the South East Asian country after he spoke out against its recent military coup and called for the release of civilian leader Aung San Suu Kyi.
British Foreign Secretary Dominic Raab on Thursday condemned the "bullying actions of the Myanmar military regime", and praised the ambassador's "courage".
Kyaw Zwar Minn told the Daily Telegraph that "when I left the embassy, they stormed inside the embassy and took it".
They said they received instruction from the capital, so they are not going to let me in.
Security forces opened fire on Wednesday on protesters in the northwestern town of Kale as they demanded the restoration of Aung San Suu Kyi's civilian government, domestic media said.
Worldwide powers have voiced anger and dismay at the junta's brutal approach, and imposed sanctions on key officials.
Global powers have voiced anger and dismay at the junta's brutal approach, but the UN Security Council has stopped short of considering sanctions, with both China and Russian Federation against the move.
"People will try to defend their own lives and their rights", said a former government minister who is part of the CRPH, a group of lawmakers representing the ousted civilian government.
A lawyer for the Committee for Representing Pyidaungsu Hluttaw (CRPH) - a group of MPs from Suu Kyi's National League for Democracy (NLD) party - met United Nations investigators yesterday to discuss alleged atrocities by the junta.
According to the Assistance Association for Political Prisoners (AAPP) advocacy group, 581 people, including dozens of children, have been shot dead by troops and police in nearly daily unrest since the coup, and security forces have arrested close to 3,500 people, with 2,750 still detained.
The CRPH says it has evidence of more than 540 extrajudicial executions and 10 deaths of prisoners in custody as well as torture and illegal detentions.
The advocacy group said 2,847 were now being held in detention.
Almost 50 of the dead were children. Myanmar's military calls Beijing a strategic partner.
An FCDO spokesperson said: 'We are seeking further information following an incident at Myanmar's embassy in London'.
Myanmar's military has since violently cracked down on opponents, with security forces reportedly killing hundreds of protesters and bystanders.
"CDM is an activity to destroy the country", he said.
"They told me that they will fight on the street and I'm also fighting my way on the stage now".
In response, some activists have started a daily two-page newsletter called "Voice of Spring", rounding up independent media reports and publishing on Twitter.