You need to be married for at least one year and be habitually resident in England and Wales. If you are not habitually resident here then both you and your spouse will need to be domiciled in England and Wales.
There is only one ground for divorce known as the irretrievable breakdown of the marriage, which is proved by one of five grounds (see below).
To file for divorce, and start the process you will need to obtain your original marriage certificate and file a petition at court citing one of the five grounds. There is a court fee of £410 to pay (January 2015).
The court will issue your petition, and your spouse must then complete the acknowledgement of service within a specified timeframe.
Providing this has been completed, you can apply to court for your decree nisi.
A judge will then consider your divorce petition and confirm that you are entitled to a divorce, listing a date for the pronouncement of decree nisi. This is the first of two decrees. It is at this stage that the court can approve any financial agreement reached between the parties.
Six weeks and one day following decree nisi, you can apply for decree absolute. This is the final decree, and legally ends your marriage.
The above is based on a typical undefended divorce. There can be complications if, for example, your spouse doesn’t return the acknowledgement of service, or decides that they wish to petition against you.