This is an area we frequently get asked about. The answer is more in the realms of a Human Resources department than payroll but we do have people that can offer general guidance regarding the statutory minimum. A worker working 5 days is entitled to 28 days paid leave, if they work for 6 days this is not increased but working less will see a pro rata reduction.
However, it can be complicated! There will be contractual considerations. Irregular hours can make life more awkward, as can sickness or maternity/paternity leave. For a definitive answer you need your HR department. If you do not have an HR department consider one of the employer legal helplines. There is also this web link –
Holiday entitlement should not be difficult but disputes can occur, it is much better to have a proper policy in place before you develop a problem.