The Prime Minister did not greet his Estonian counterpart outside the door of Number 10, seemingly to avoid journalists ahead of the confidence motion on Monday night.

Estonian prime minister Kaja Kallas was visiting Downing Street to speak to Boris Johnson about strengthening the Nato alliance against Russian aggression, and she did not receive a handshake outside in a marked break from protocol.

Ms Kallas instead waved to cameras on her entrance and spoke briefly with the press after their meeting, which lasted around 20 minutes and was mostly in private.

Kaja Kallas visit to UK
The two leaders met at Downing Street on Monday afternoon (Alberto Pezzali/PA)

The Estonian leader tentatively told the media that Mr Johnson was in “good” spirits.

When asked by the PA news agency how Mr Johnson appeared to be feeling, Ms Kallas paused for a moment before saying: “The mood was good.”

While inside, Ms Kallas thanked Mr Johnson for his “great leadership” on the world stage against Vladimir Putin’s aggression in Ukraine.

She said: “We have been great allies in Nato and we are very grateful for the British troops in Estonia, and also that you have doubled them while the war took place.

Kaja Kallas visit to UK
Boris Johnson speaking with Estonian Prime Minister Kaja Kallas inside Number 10 after avoiding greeting her at the door (Alberto Pezzali/PA)

“I also thank you for the great leadership in fighting with Ukraine and giving them all the help they need.

“I think the UK has been a very leading voice on the world stage so that the moral compass would be correct in this regard, so thank you for that.”

Mr Johnson said it was a “great pleasure” to welcome Ms Kallas and praised her on the “outstanding job” she is doing standing up to Mr Putin.

He added: “We’re very proud of the friendship that we have with you in Estonia and we’ve got a lot to talk about, a lot more to do.”

The leaders previously met at a Nato military base in Tapa, Estonia, on March 1, and Monday marked their fourth meeting of the year.

Number 10 said the UK has sent an “additional battlegroup” to Estonia, which shares a 182-mile border with Russia, to ensure its security and stability.

A spokeswoman for Downing Street added: “Discussing the importance of the Nato leaders’ summit later this month, both leaders denounced Putin’s abhorrent invasion of Ukraine, and the Prime Minister said the Russian president was the author of his own embarrassment.

“The prime ministers said there could be no backsliding in Allies’ support for Ukraine.

“They were also clear that Nato needed to agree a strengthened position in the face of continued Russian aggression.

“The leaders agreed to stay in close contact in the coming weeks.”

During her visit to London, Ms Kallas was also presented with the Grotius Prize, named after a philosopher regarded as having founded some core principles of international law, by Policy Exchange, a Conservative think tank.