Probate and letters of administration are not always needed. I've just been looking into this for a friend who was expecting an inheritance when her mother died, two years ago. We applied to the probate office for a copy of the will and they replied that no will had been presented to the probate office. On the back of the form was a list of possible reasons, including, "from the CAB website":
"You usually need probate or letters of administration to deal with an estate if it includes property such as a flat or a house. Otherwise, you may not need probate or letters of administration if:
1. The estate is just made up of cash (that is, bank notes and coins) and personal possessions such as a car, furniture, and jewellery.
2. All the property in the estate is owned as beneficial joint tenants This property automatically becomes wholly owned by the other owner
3. You had a joint bank account
4. The amount of money is small
5. You discover that the estate is insolvent, that is, there is not enough money in the estate to pay all the debts, taxes and expenses
6. there are certain life insurance policies and pension benefits in the estate."
In my friends case clauses 2 & 3 seem to what has happened and her stepfather may now change what were mirror wills, to the benefit of his own son and exclude his step-daughter..