A Deed of Variation lets the beneficiaries of an estate agree, within two years of death, to redirect some or all of an inheritance to someone else, such as grandchildren or a charity. For Inheritance Tax and Capital Gains Tax purposes, the change is read back to the date of death, provided the deed is correctly drafted.
Every affected beneficiary must consent, which means a Deed of Variation cannot be used to redirect an entitlement away from a minor or a person lacking mental capacity without court involvement, nor can it help once an estate is fully distributed or once the two-year window has passed.
Because it depends on unanimous agreement and careful drafting, a Deed of Variation should never be relied on as a substitute for keeping your Will properly up to date.