Under the Working Time Regulations 1998 (WTR 1998), SI 1998/1833, reg 4(1) unless a worker opts out of their rights, their working time, including overtime, in any reference period that applies to them, must not exceed an average of 48 hours for each seven days. For more information, see the section of Practice Note: Hours of work and working time entitled ‘The maximum working week’. It is possible for employers and workers to agree that the worker will work more than 48 hours a week. In order to be valid, an agreement must: • be in writing