Mirror wills are the most common type of will made by married couples and civil partners. They are called mirror wills because they reflect each other — each partner leaves everything to the other, and then to the same beneficiaries on the second death.
The Limitations of Mirror Wills
The main limitation of mirror wills is that the surviving partner can change their will after the first death. There is nothing to prevent the survivor from making a new will that leaves everything to a new partner or excludes the children.
Mirror wills are not the same as mutual wills. Mutual wills are contractually binding — the survivor cannot change their will after the first death without breaching the contract.