The legalities and your rights to marry abroad

For a religious marriage, the Banns must be called on the three Sundays prior to the wedding. For a civil marriage, you are required by law to give notice of marriage (at your local registry office) and this must be given 15 clear days before the marriage can take place. Once given, your notice is valid for 12 months.

Overseas marriages are legal in the UK, provided they comply with the laws of the country you get married in. However, overseas marriages cannot be ‘registered’ here in the UK except if one of you is serving in, or attached to, the British Armed Forces.  

If you have any general enquiries about marrying abroad, you should contact the Embassy or High Commission of the country concerned. It is possible you will be asked to obtain a certificate of no impediment. This is a document required by some foreign authorities to enable a non-national to marry in their country and, under certain circumstances, can be provided by your local register office.  If you are asked to provide one, you should contact your local register office.To find details of your local register office, visit your county council (or London or Metropolitan borough) website. 

For more information:
http://www.weddingchaos.co.uk/wedding-abroad/wedding-abroad-legal.asp