The ATS unit I'm working at rosters a one man shift to handle Ground, Flight Data, Tower & Procedural without an assistant and we're not subject to CAP670, neither are we subject to any other working time regulations. We also work a split shift system (2 one man shifts contained within the same 24hr period). It's no-one's idea of an ideal system but due to staff shortages and the need to get time off at some stage, it's all we can do.