Section 18 of the Wills Act 1987 (as substituted by s18(1) of the Administration of Justice Act 1982) states that the marriage or civil partnership of a Testator automatically revokes any will that was made before that marriage. The ‘in contemplation of marriage’ clause is an exception to this rule, and means that if a Testator expects to be married to a certain person at the time the will is executed) then that will shall not be revoked when the Testator does eventually marry.
This exception will be effective provided that two conditions are met. The first condition is that the testator must have been expecting to be married or to form a civil partnership with a particular person at the time that the will is executed. It is not enough for the testator to simply state that he or she expects to marry in general. This was expressed in the case of In Re Coleman (deceased)  1 All ER 675. In this case the testator had made certain bequests ‘unto my fiancée Mrs Muriel Jeffrey’ whom he later married. The court held that the use of the word ‘fiancé’ or ‘fiancée’ would normally express a sufficient contemplation of marriage to that person.
The second condition is that it must appear from the will that the Testator intended that the will should not be revoked by the marriage or formation of a civil partnership. It is therefore preferable for these wishes be included in writing within the will. For example, a suitable clause to be written into the will would be: “At the time of making this will, I expect to be married to (insert name) and intend that this my will shall not be revoked by my marriage to the said (insert name)”. If marriage or civil partnership takes place to any person other than the person stated in the will, then that will shall be revoked.
The clause should really only be considered temporary as there is always a risk that a relationship may break down and a Testators wishes will therefore change. After marriage or civil partnership has taken place it is often desirable (but not essential) to redraft a will, in order to reflect a couples new status.