Britain has joined most of the rest of Western Europe in becoming a military protectorate of the United States.
The UK has a formidable, independent nuclear force based on the Trident missile system. Any potential aggressor, such as Russia, would be foolish to attack the UK and risk retaliation by this force.
That actually occurred in 1940 when we “Lend Leased” them a flotilla of destroyers and the U.S. Navy joined in the secret war with Germany’s U-Boats. They won’t be happy admitting it but Britain’s been living under our wing to some extent ever since. There ought to be a drinking game for every time the word SPAM is mentioned during films about wartime Britain. And to be fair, America prospered while the Royal Navy patrolled all seas and allowed an age of unparalleled peaceful trade.