These days there is a growing trend of getting married outside the UK in an exotic location, and many travel firms offer wedding packages. They typically deal with all the paper work for you, and one of the documents you need is an apostille. An apostille can authenticate any document and is proof that the information contained in the document is genuine.
If you are unsure about whether you need an apostille or not, you should check with the firm organizing your wedding. The apostille is recognized as proof of the attached document's legality. In all countries that have signed up to the Hague Convention, and no other authentication is necessary.
To marry abroad you usually require your birth certificate authenticated; if you have been married previously, then a death certificate of your late spouse will also need authenticating, or a degree absolute. You will also need a certificate of no impediment. This will take several weeks to obtain as before one is issued, a public notice must be posted. You may also need an affidavit authenticated, proving that you are free to marry. You can apply for a certificate of no impediment from your local registry office.
Different countries have different requirements and you would do well to check with the embassy of the country you intend to marry in before the wedding.
Don't leave it until the last minute before trying to get an apostille, as it normally takes 5 working days for one to be issued. However, there are different delivery services that will determine the delivery time.