A mutual will is a type of will where two or more people make wills which they agree with each other not to change.
Once the first person dies, the survivor is bound by a constructive trust to give effect to their agreement. Mutual wills are usually in the same terms and confer reciprocal benefits. The agreement not to change the wills can be orally or in writing. The agreement is often incorporated into the terms of the will itself.
The rational for mutual wills is that the testator wants to ensure that intended beneficiaries inherit assets when the surviving partner dies. In practice, however, this can lead to problems as mutual wills are inflexible and cannot be changed (which is contrary to the principle that a person can amend their will as they see fit). Complex litigation can ensue if the survivor falls out with the beneficiaries.
The key element is an agreement not to change the wills and whether such an agreement has been reached is often the subject of disputes.
In Re Goodchild  3 All ER 63, Lord Justice Leggatt stated:
“A key feature of the concept of mutual wills is the irrevocability of the mutual intentions. Not only must they be binding when made, but the testators must have undertaken, and so must be bound, not to change their intentions after the death of the first testator. The test must always be, ‘Suppose that during the lifetime of the surviving testator the intended beneficiary did something which the survivor regarded as unpardonable, would he or she be free not to leave the combined estate to him?’ The answer must be that the survivor is so entitled unless the testators agreed otherwise when they executed their wills. Hence the need for clear agreement.”
If a survivor does change a mutual will, the personal representatives under the new will would hold the assets on trust in accordance with the terms of the mutual will.
Legal advice should be sought on this complex area. Paul Davis, Partner at BHW Solicitors, regularly acts in respect of contentious probate disputes and can be contacted at firstname.lastname@example.org.