The Government have issued no such guidance. The Employment Equality (Religion or Belief) Regulations 2003 outlaw discrimination, harassment and victimisation on grounds of religion or belief at work and in vocational training.
Under the regulations employers are not required to ban discussions about religion or belief in the workplace. However, the ACAS good practice guide sets out some broad guidelines that employers can follow. This includes making staff aware that if their discussions cause offence then this may be considered to be harassment and therefore unlawful, potentially leading to dismissal. The Business Link website also provides additional information for employers.