yeah basically, uk is one of a handful of nations on the planet with a guaranteed fatal second strike.
the nuclear subs are invisible and effectively invincible. (you cant take out the mainland and the invisible nuclear subs at the same time). the uk also has 200 nuclear weapons, and if you take out the mainland and completely level the entire united kingdom, you still have vanguard class subs firing 40 warheads at your capitals and major cities from unknown locations anywhere on the planet.
The missiles are 13 metres (44 ft) long, weighs 58.5 tons (130,000 lb), has a range of 11,300 kilometres (7,000 mi), a top speed of over 21,600 km/h (13,400 mph) (Mach 17.4) and a CEP accuracy to within "a few feet".[37] It navigates using an inertial guidance system combined with star-sighting, and is not dependent on the American-run Global Positioning System (GPS).
The British Trident warheads are capable of selective yield, ranging from under a kiloton up to the full yield of 100 kt (around 7 x hiroshima).
nuclear rain guaranteed.