About what?

You seem convinced that the UK is more likely to suffer an attack from an advanced nuclear power, such as Russia, than it is an attack from an unconventional power (a non-advanced state or a state-less group).

It was, and is, and unless you're hiding some pretty impressive research it always shall be. The fact that ports and harbours are a possible vector for terrorist attack doesn't reinforce your assertion that this is the most likely attack vector that the UK will face.

I don't think it's "the most likely attack vector that the UK will face". I think that would be a simple bomb in an airport security queue, shopping centre, or transport system.

I do think it's the most likely way a western power will suffer a nuclear attack though. I'm happy to admit that's pure speculation on my part though since, like you, I don't have the gift of clairvoyance.

I don't think it's that far-fetched given that the current point in history though: the physics and engineering knowledge is readily available, the often sketchy dissolution of the USSR's nuclear stockpile, the presence of small groups with with an eye for big impact attacks, the fact that every country rich enough to have a missile-based nuclear weapons programme values its own economy more than it hates its "enemies", and the fact that globalisation has bound the world's economies more closely than at any point in human history.

Russia may go full Putin and try and conquer half of the EU and trigger WW3, or Putin may die and it may turn into a democratic peace loving nation. We do not know. The threat from terrorism may grow, or it may be much reduced over the coming decade.

I suppose that's true, then again you don't need to plan that far ahead in the future if you want to be a terrorist.

You do need to plan fairly far ahead if you want to try and conquer half a continent and, unless you plan to undo the internet/mobile phones, you're never going to hold it unless those people want to be conquered.

Ah, so you think there are no, and never again will there be, any existential threats to the United Kingdom?

That sounds like a trick question. I don't think it's likely that the UK will suffer a nuclear attack from the US, France, Russia, China, Israel, Pakistan, India, or a similar entity.

I think it's more likely that the UK, or some other western power, will suffer a nuclear attack from a small group like Al Qaeda either operating off their own bat or receiving covert assistance from an unstable state.

I think it's extremely unlikely that that kind of attack would be deterred by us possessing Trident.

Take today's bogeyman, Isis. Let's say they decided to carry out a nuclear attack on the West (the US, UK, France, Germany, whoever). They're not going to do so via a missile, nor are they going to give a shit that you could fire a missile back - where would you fire it?