UK varies from unit to unit, fortunately UK rules and regs don’t allow the daft working hours we see US ATC doing. The unit variation comes in with number of staff, and hours of operation. There’s a UK industry shortage of ATCO’s, so some units have hours of operation based around the number of staff vs primary customer needs.
The UKs hours regulations were SCRATCOH, but I can’t find an easy link to them, these went to Easa, but since coming out of the EU, the UK is back on its own formula which can be determined by each unit, however they are ideally based around SCRATCOH/Easa as they are practical and on the whole safe frameworks to hang rosters on.
The link below gives a good idea of the parameters within the system.
https://skybrary.aero/sites/default/...helf/34421.pdf