Thanks for your question, I'm sorry for your loss.
Any assets that your father held in joint names (Eg, bank accounts) with his partner will pass automatically to her, this may include the house they bought together if they held their interests as joint tenants. If they held their interests as tenants in common then his interest will pass according to the intestacy rules.
You can check by downloading a copy of the register for the property from the Land Registry by paying a £4.00 fee:-
Look at the proprietorship register of the title you have downloaded from the Land Registry (where the proprietors of the property are listed). If the following entry is immediately below the named registered proprietors then the interests are held as tenants in common:-
" No disposition by a sole proprietor of the registered estate (except a trust corporation) under which capital money arises is to be registered unless authorised by an order of the Court"
If there is no such entry then the property is held as joint tenants.
Other property that is not held jointly will pass under the intestacy rules, which means that it will go to his children. Please let me know if one of his children has predeceased him.
His partner may be able to make a claim on his estate under the Inheritance (Provision for Family & Dependents) Act 1975, but she would need to instruct a solicitor to do this.
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