The Certificate of Approval (COA) was introduced by the Home Office on 1 February 2005. This immigration document serves as permission to get married or form a civil partnership in the UK and is used in lieu of traditional fiancee or visit for marriage entry clearance issued by British Consulates abroad. Non-EEA and Swiss nationals are unable to apply for a Certificate of Approval from outside of the UK as it specifically relates to those applications made from people already in the UK.
Those non-EEA and Swiss nationals already in the UK wishing to marry or enter into a civil partnership, are required to give a notice of intention to marry to a designated Register office where the marriage will take place. The registrar will not be able to accept your notice of marriage and you will not be able to marry or form a civil partnership, unless you obtain a Certificate of Approval from the Home Office.
Prospective applicants usually must have at least six months validity on their leave to enter and three months minimum leave remaining. In some cases, however, those who hold short term visas and subsequently are authorised to remain in the UK for less than six months (e.g. visitor visa holders) may be eligible to apply for a Certificate of Approval. Pursuant to the judgment of the High Court on 10 April 2006 and the Court of Appeal decision on 23 May 2007, the Home Office is currently accepting the COA applications from those visa holders who are granted six months leave to remain or less, and have less than three months leave remaining. However, such cases are processed under stricter rules and applicants may be required to submit additional information in order to gain a Certificate of Approval.
You are not required to obtain a Certificate of Approval if you are a British citizen, member of the European Economic Area (EEA) or Swiss national; are not an EEA national but have a family member that is; have the right of abode in the UK clearly stamped in your passport, or are not subject to immigration control for an officially granted reason.