Can employers require employees to take a proportion of their annual leave during a manufacturing stoppage due to a downturn in demand?

Yes. In the absence of any agreement to the contrary, under reg.15 of the Working Time Regulations 1998 (SI 1998/1833) an employer can give an employee notice of the requirement to take all or part of their statutory annual leave on certain dates. The length of the required notice is at least twice the period of leave that the worker is required to take. In relation to any contractual holiday entitlement over and above the statutory minimum, the employer is able to determine its own rules and procedures about how and when leave can and should be taken.