Sideways disinheritance happens when your assets pass to your spouse, who later remarries, and everything ends up with their new partner’s family. Your children get nothing. It is one of the most common estate planning failures in the UK.
The root cause is usually joint tenancy — when one spouse dies, the survivor automatically owns the entire property. If they remarry and leave everything to the new spouse, the original family’s inheritance vanishes. The fix: sever the joint tenancy to become tenants in common, so each spouse’s share passes through their Will.
A life interest trust is the standard protection. Your share is held in trust — your spouse can live in the property for life, but when they die it passes to your children, not a new partner. It protects the survivor’s home while ring-fencing the next generation’s inheritance. The planning must happen before the first death — after that, it is too late.