Can an employer refuse a request for annual leave during an employee's notice period?

Yes. As at any other time, the employer can consider whether or not the employee's request for annual leave is compatible with the needs of the business and can refuse it, as long as it does so in line with its annual leave policy. The employer should act reasonably when considering the request. It should also take into account that it will have to pay the employee in lieu of any untaken holiday entitlement on the termination of their employment. Therefore, it may be cost effective for the employer to allow the employee to take holiday during their notice period.