British soldiers will be deployed to defend Sweden and Finland if they are attacked by Russia, Boris Johnson has said.

It came as he unveiled historic defence pacts with the two countries, which have both been threatened by the Kremlin in recent weeks following their interest in joining NATO. Despite both countries having sent weapons and aid to Ukraine, neither are members of the alliance, meaning they are not covered by Article Five, which says an attack on one member is an attack on all.

Asked during a press conference alongside Finnish president Sauli Niinisto if there would be “British boots on the ground” on Finnish territory during a “possible conflict with Russia”, he said: “I think the solemn declaration is itself clear. And what it says is that in the event of a disaster, or in the event of an attack on either of us, then yes, we will come to each other’s assistance, including with military assistance. But the nature of that assistance will of course depend upon the request of the other party”.

He also said the UK would be prepared to offer Sweden “whatever Sweden requested”, if Moscow went through with its threats of a military offensive.

“There is no doubt at all looking at what Vladimir Putin has done, that this, if it were not to be resisted, this would not be the end of his neo-imperialist, revanchist, ambitions. And just imagine the consequences, not just military or political, but economic, of further Russian aggression against any of the other former parts of the Soviet Union. It’s to prevent that further catastrophe that it’s important we are strong now. Russia’s invasion of Ukraine has opened a new chapter in post-Cold War history - after the UK agreed the defence pacts”, - added Johnson.