If you are planning on getting married outside of the UK you may be requested to provide a certificate of no impediment. This certificate is requested as evidence that you are allowed to marry. It is common practice and quite simple to acquire.
The certificate of no impediment is issued in the UK by the local register office (registry office). The registrar will place a notice in the office of your intended marriage. If no objections are received the certificate of no impediment will be issued after approximately 3 to 4 weeks. The fee is typically in the region of £30 to £40.