Think it's about time we went all in on defence rather than holding these weapons ourselves.
You think people haven't thought of this before?
Those who threaten us don't care about their own people and also have mentally unbalanced beliefs about what would happen if they did. Apocalypse is the only outcome.
Putin and his ilk don't have a death wish even if they don't care about their people. They also don't want to rule over nuclear cinders. It rather defeats the purpose of being a dictator.
Ensure we can shoot them out of the sky
Which is extraordinarily difficult. Especially once you're dealing with hundreds of independent warheads and thousands of penetration aids. The number of interceptors required increases almost exponentially compared to the number of warheads you have to destroy. This all assumes that you have a system that can reliably intercept ballistic targets of course. Again, do you seriously think people haven't thought of this before?
detect rogue portable weapons
I look forward to the delays at the points of entry to the UK as you conduct radiological screening of every container being unloaded, every cargo pallet taken off an aircraft, every lorry exiting a ferry.
and have enhanced capabilities such as the ability to nullify ships and submarines.
What on earth do you think the point of a navies are? That's quite literally one of their primary missions...
Couple this with crack squad teams positioned throughout the world whose sole mission is to survive and enact total revenge on any individuals who have used nuclear weapons.
If Putin knew that even if he survived in his bunker that he and those he cared about (if there is anyone) would live only terrible traumatic lives afterwards, that may be the only defence worth having.
Putin already knows he's dead in a nuclear exchange. There is no bunker yet built that cannot be dug out by nuclear ground bursts. There's a reason why the US Strategic Air Command flew an airborne command post 24/7 during the Cold War (and why the US still maintains aircraft capable of fulfilling the mission) despite having extensive bunker facilities at places like Cheyenne Mountain and Offutt Air Force Base. It's because they know that all those facilities are going to be radioactive holes in the ground shortly after the start of nuclear hostilities.
That's quite apart from the fact that these "crack squad teams" would represent the invasion of Russia and the start of a war by the the US/NATO.