The United Kingdom has promised to defend Finland and Sweden if either coutnry is attacked by Russia before they join NATO.
British Prime Minister, Boris Johnson made the promise during a tour to the two Nordic nations on Wednesday, May 11.
He met first Swedish Prime Minister Magdalena Andersson at her official countryside residence; then Finnish President Sauli Niinistö in Helsinki, Johnson pledged mutual defense while Sweden and Finland make moves to join NATO following Russia's invasion of Ukraine on 24 February. 
Finland shares a 1,340-kilometre land border with Russia, while Sweden doesn't have a land border but has strategically important islands in the Baltic Sea close to the Russian exclave of Kaliningrad. Russia has threatened to make military moves if either countries tries to join NATO.
The new agreement will “fortify northern Europe’s defenses, in the face of renewed threats,” Johnson said in a statement.
“These are not a short-term stop-gap, but a long-term commitment to bolster military ties and global stability, and fortify Europe’s defenses for generations to come,” Johnson said in the statement.
Johnson says the deal will also deepen ties between the British military and the Swedish and Finnish armies.
Should Sweden and Finland apply, there will be an interim period between the application and all 30 NATO members’ parliaments ratifying their membership. That process could last anywhere between four months and a year. 
"The Russian invasion of Ukraine has changed the equation of European security. It has re-written our reality and re-shaped our future," Johnson said at a Helsinki press conference.
Answering a question about how Russia should feel about Finland's possible NATO membership, President Niinistö said "you caused this. Look in the mirror."