Yes. Your written statement of particulars of employment, which you must be given on or before your first day at work, must state which days of the week you are expected to work.
The written statement must also tell you whether these day may vary and if so how, and what method will be used to allocate your hours and to tell you about them (for example, how you will be notified about shift changes or cancellations, and how much notice you can normally expect).