Required self-study time for BSc. Mathematics and Physics course

UK universities usually assume you will spend roughly the amount of time equivalent to a full time job on your studies, including lectures and tutorials and labs. So anticipate spending 30-40 hours a week on your course in total (including timetabled activities).

Usually the most successful students approach things as a 9-5 job and just consistently turn up to campus at 9 or so each morning and spend the day on campus working on their assignments, doing further reading and practice etc, between their lectures and labs and other timetabled activities.

This leaves a fair bit of time for societies and so on, particularly if you factor in that Wednesday afternoons at most UK unis are left free of timetabled activities to facilitate students participating in societies and sporting activities etc.

It's usually possible to work part-time while studying full time but it's generally recommended to not work more than 8-12 hours (I would say 15 max...) a week in order to ensure you are devoting enough time to your studies and to avoid burning yourself out. Obviously though working hours tend to come at the cost of societies and other cocurricular activities.