I've looked at a view, PCloud, IDrive, Acronis True Image etc. and it seems most of them, even if you click on the UK version are worldwide companies. Whether that means each country, or sector has it's own Cloud I have no idea.
Sometimes a website will tell you where the servers are located, but you might have to dig around a bit. Try the FAQs, or alternatively the privacy policy might refer to cross-border data transfers and the jurisdiction they operate under. If you can't find it, you can always try asking direct.
I don't know how much space I need?
What do you want to back up? Photos and music need quite a lot of space, text files don't. Most providers will give you some idea of what each tier can handle, and usually there's a free starter level which you can use to try the service out before deciding whether to progress to a paid level with more capacity. With one of mine there's no free tier, but as it's a monthly rolling contract I wasn't locked in to a long contract that might not have been suitable.
I'm prepared to pay but not an extortionate amount
Me too - but cheapest isn't always best. I've tended to look at longer-established/better known companies, or up-and-coming ones that get good reviews. I currently have a small free package at a newer firm, and a paid one at a more established one. Cheaper tiers sometimes restrict the number of users, which might be an issue for some people.
I don't know what kind of security/encryption I need. I assumed that all the different Cloud providers have good security/encryption.
I'm not an expert on this, and others might like to weigh in. The gold standard (I think) would be for everything to be encrypted before it leaves your computer (though this can slow down transfers) and for no-one in the company or data centre to be able to access your files under any circumstances. However, encryption in transit tends to cost more, and in the end I decided that I wouldn't use these services for ultra-sensitive items.
I would prefer UK/Europe jurisdiction, but then we all use Microsoft and Google and they're US based.
Me too. As I said, my requirements aren't the same as yours - because my broadband isn't very fast I decided to rely on backups on demand, rather than running continually in the background. The ones I've chosen are Icedrive (UK company) and HiDrive from Ionos (formerly 1&1 - German) - they seem to work OK for me, but obviously your needs will be different.
