The written statement of particulars of employment, which should be given to employees within 8 weeks of starting work, should include "details of terms and conditions of employment relating to hours of work and normal working hours".
In order to avoid confusion normal hours should be specified. There is a common law duty on employees to work some overtime. This requirement may be stated in more detail in your contract of employment. However, the requirement to work extra hours must be reasonable, and would still be subject to the limits imposed by the Working Time Regulations.
If you are having problems with unwanted overtime you should speak to your manager, if you feel that you can. You should also take advice from your union if you have one.
