The Employment Equality (Religion or Belief) Regulations 2003 outlaws discrimination in employment and vocational training on grounds of religion or belief. Religion or belief is defined as any religion, religious belief or similar philosophical belief. There is no specific list but does include all major religions as well as those less widely practiced ones.
The Regulations do not say that employers must provide time and facilities for religious or belief observance in the workplace. However, as an employer, consideration should be given to your policies, rules and procedures in order that they do not indirectly discriminate against employees of particular religions or beliefs. An employee may request holiday in order to celebrate festivals and attend ceremonies and where this is reasonable and practical this request should be considered sympathetically.