If you want to run around in really bad weather, that's your call, if you want to stay at home feet up and dry, again personal choice.
If it's shitty weather with 2 wheels you jump off the bike, strip off the gear and not spend 8 hours cold and wet.
I don't choose to get soaked through with this hobby, if it comes out of nowhere you deal with it, but if you know it's gonna be really bad and unless you get a kick from it, there's no shame in not feeling miserable.
TL;DR This is the UK, prepare for unexpected rain, but remember it's just a game we're playing; if you're not having a good time, then where's the fun?
-----
Before anyone thinks I'm a fair weather rider, I've never owned a car (don't even have a car license) and I'm in my 40s, and have done the Elefant Rally in Germany a couple of times (Google Elefantentreffen if you don't know what I'm talking about) ? .