Workers are not entitled to insist on taking annual leave during periods when they would otherwise be working. An employer can require leave to be taken during inactive time in a particular work pattern, provided the employer satisfies the statutory notice requirements.
Employees whose working pattern involved two weeks on duty followed by two weeks off were not entitled to insist on taking statutory holiday during periods of time rostered to be working. The employer's denial of such requests was valid; there was no requirement to set out in advance the periods during which employees would be permitted to take leave.
However, it is best practice to confirm the periods when leave can be taken either in the contract of employment or in an annual notice. (Craig v Transocean International Resources, EAT )