Question for the British...

Hello, British people or anglophiles....or those living in the UK....or just those that watch a lot of BBC shows,

What's the go-to fake phone number on TV dramas? I know that in the US, it's any number that's 555-XXXX. What do British shows do?

I need to put a number in the demented'verse because one of my British characters actually has a phone - but I don't want to accidentally put in a REAL number. So, I need something that looks believably like a regular number, but is fake.

Thanks!