Re: How to keep us safe...
I'm sure Ukraine are dead glad they gave up their nukes. That's turned out fine for them hasn't it?
As for cruise missiles, we could do it. There is/was a US nuclear version of the Tomahawk - but that's been withdrawn as part of the 90s nuclear treaties. I don't know whether they've kept any in storage, and just don't deploy them. Our hunter-killer subs carry Tomahawk - and of course we could build a bigger attack sub to fill full of cruise missiles, as they're useful in operations like Libya - and then equip that with some nuclear ones. From memory it's got a range of over 1,000 miles.
Or we could build one specially, we've got decent missile tech nowadays. Or an air-launched cruise missile. Or both.
I just happen to be reading Peter Hennessey's history of the Royal Navy submarine service at the moment. So I know that when they ordered Polaris, the other options were an air-launched cruise missile and a submarine launched one. They worked out it needed 4 subs to carry Polaris, with one always at sea - or 7 subs with cruise missiles - which could be used for other stuff as well. And even that was a worry, as if you're using them, then they're much more detectable - so ideally you'd need more. Which is why they decided on Polaris.
For every 4 subs/ships you own, you expect one to be in long term refit and at least one other to have broken down or be undergoing more minor maintenance. Which leaves one for training/spare and one you're actually using.
That was also before anti-air missiles were capable of shooting down other missiles. So you'd need a lot more cruise nukes. Long range ones are slow, they're just small aeroplanes after all, but you need range as you're firing from the sea. That makes them much more detectable.
Air launched is easier, but then you need to get your aircraft within range of wherever you need to shoot at. And that means forward bases, then fighters to protect those and jammers and tankers. And you're still going to get many of those cruise missiles shot down.
Obviously you could use carrier based planes, but then we'd need several more carriers. And escorst to protect them.
So basically anything other than ballistic missiles means we'd need to seriously expand either the navy or RAF. And that would cost much more than 4 subs.
Then you get to the cheaper option of having your ballistic missiles on land, as opposed to at sea. Land based ones are much more vulnerable to a surprise attack - whereas an at sea deterrent has historically been much harder to deal with. And can return fire after the UK has effectively been destroyed.