I can't really say much about the after approval timeline but:
waiting for NOA2 - approval - takes about 8-10 months on average right now. It applies to everybody, no matter where you're from!
After approval, at this moment it takes about 2-3 months to be sent to DOS. Your location also doesn't matter for this!
(The speed can change at any time, depending on how fast USCIS works!)
So this is for the USCIS part. After that, maybe someone from UK can add more but from what I've heard the UK embassy is not too backlogged so it shouldn't take that much longer!