As religious work falls within the definitions of charity work in the UK, the Immigration Rules for regions workers fall under the rules for Tier 5 temporary / charity workers. This visa category is designed for individuals looking to migrate to the UK for the purpose of undertaking voluntary work for a charity. It is important to stress that the work must be for the sponsor's organisation.
It should also be noted that individuals under this visa category must only be engaged in voluntary activities not receiving any payment for their work (charity - as the name implies).
In order to successfully assign the certificate of sponsorship, the sponsor must guarantee:-
Visa is granted for a maximum period of 12 months, or the time given on the Certificate of Sponsorship plus 14 days after the end date given on the Certificate of Sponsorship and up to 14 days before the start date, whichever is the shorter.
If you are outside the UK, you may have to apply for entry clearance (visa) to the British Embassy/High Commission/Consulate before you can come to the UK under Tier 5 (Temporary Worker - Charity Workers) category.