I already know this, it doesn't change anything. Who is able to blockade the UK's access to oil, gas or uranium, all of which are much easier to stockpile than electricity? The only one with that capability is the USA. Who is able to attack a HVDC line? Anyone with a fifth rate navy.

Pretty sure UK needs to import uranium, too.

That's a false argument. Uranium gives you power for years, and can be sourced from multiple sellers. That is very different from a line that the other side or a third party can simply cut. Point in case: NordStream pipelines that supplied Germany.