When someone dies without leaving a will, this is called 'intestacy'.
Once it has been established that there is no will, an administrator is appointed (court approval isn't needed if it's only a small estate) to distribute the estate to surviving family members according to the rules of the Administration Act 1969.
The deceased person's "estate" is all their property, including their personal possessions (like clothes and jewellery), money in bank accounts, any house or other land they own, proceeds from insurance policies, and shares in companies.
The deceased's estate won't include any property that he or she owned jointly with a partner, like a house or bank accounts.
As they owned them jointly this means that when one of them dies the other becomes the sole owner.