Ukraine’s ambassador to the UK has said the country could consider dropping its ambition to join Nato to avoid war with Russia.

Vadym Prystaiko told BBC Radio 5 that the country would, due to threats and blackmail, consider “serious concessions” including removing the goal of joining the Nato alliance from the Ukrainian constitution.

It comes as armed forces minister James Heappey warned against extending Nato’s “collective security” to a non-member and Boris Johnson is due to join last-ditch diplomatic efforts in Europe.

Nato has always been a defensive alliance that sovereign nations have chosen to join for their collective security. Nato does not attack others.

Mr Heappey said the deterrence of Russia needed to go beyond economic sanctions, but that Nato’s “defensive” operations were “very different” from offering its collective security to a non-member “especially with the very real possibility that the alliance fractures as a result”.

Writing in The Times, Mr Heappey said: “Nato has always been a defensive alliance that sovereign nations have chosen to join for their collective security. Nato does not attack others.

“Since the fall of the Berlin Wall, Nato has deployed beyond its borders to Afghanistan in response to an attack on the United States; played a role in counterinsurgency and counterpiracy missions in sub- Saharan Africa, Iraq and the Indian Ocean; and played an important part in stabilising the Balkans after the break-up of the former Yugoslavia.

“I would argue, however, that these are all very different from offering the collective security of the alliance to a non-member especially with the very real possibility that the alliance fractures as a result. It would also be exactly the pretext Putin needs to claim that he’s responding to western aggression on his borders.”

As Ukraine is not a Nato member and allies in the defence alliance have said they would not join fighting in Ukraine but have bolstered forces in neighbouring nations and are threatening widespread sanctions.

Downing Street conceded Moscow could be planning to invade “at any moment” but the Prime Minister will hold talks with world leaders before a trip to Europe during this week’s “window of opportunity” for de-escalation.

The UK and other Nato allies have urged their citizens to flee Ukraine and some airlines have cancelled flights to Kyiv amid growing concerns that the estimated 130,000 Russian troops amassed on the border could be poised to attack.