The rules of intestacy are followed when you don’t have a valid will. In these circumstances the state prescribes who should inherit your estate. This usually means that family (parents, children, siblings or cousins) receive everything you own, in a specific order and in specific shares.
The big problem with intestacy is that the rules cannot be adapted, and people you may expect to inherit something do not. For example, if you separated from a spouse years ago but are not yet divorced, they are still in line to inherit... even if you have been living with a new partner for years. Your new partner, on the other hand, would be left empty-handed.
If you make a gift to one of your children during your lifetime, on the condition that other children should inherit more, again, unless this is in your will, the rules of intestacy cannot take this gift into account and your estate will be divided equally.
If no surviving relatives can be found then your whole estate will be passed to the Crown Estate. The Crown Estate will probably gift everything to HMRC. If this isn’t your intention or wish then the only way to protect your estate is to make a will.
For more information on the Rules of Intestacy please see the Government’s guidelines.