For a marriage to be lawful and comply with UK Civil and Church law, Banns must be read out in church. Banns are just an announcement in the local parish church of your intention to marry and a chance for anyone to put forward a reason why the marriage may not lawfully take place. Banns need to be read in the parish where each of you lives as well as the parish church in which you are to be married, if that is somewhere else. You must have your banns read out in church for three Sundays during the three months before the wedding. This is often done over three consecutive Sundays but does not have to be.
You will probably wonder what all the fuss is about with Banns, it is an archaic practice which hardly makes any sense at all in modern times, but nevertheless we have to do it because it is ancient law. Once upon a time people would have know who the people were who were getting married and they would know if there was a valid reason to object to the marriage. The reasons are quite specific and include such things as the bride and groom are blood relatives, or already married to somebody else. It is nothing to worry about and it can be quite nice to come along to church and hear you name read out, so come along if you can.
If there is not enough notice given for the Banns to be read before the marriage is due to take place, or in the case of the marriage of people whose nationality is not British, or if one or both of you do not live in England, it is recommended that a Marriage Licence is given instead of Banns. This is especially recommended if there is any doubt as to the legal requirements of the home country of a non-British person for recognition of an English Church marriage.