Thanks for your question.
I assume there is not fraud or capacity issue in the making by your father of his will.
If no provision has been made by your father for you then you may be able to make a claim against the estate under the Inheritance (Provision for Family and Dependent) Act 1976. You must make the application within 6 months of the date of the grant of probate in the estate and you will need a solicitor to do it for you.
The Court will consider what is a "reasonable financial provision" for you and will take a number of factors in to account in determining what is fair (eg. size of the estate, other claims, resources and needs of other family members/dependants, responsibilities the deceased had to you), each case turns on it's own facts and there are no hard and fast rules to work out what you are entitled to without taking full and detailed instructions.
It would be folly for me to predict whether you would be successful without be having received you detailed and specific instructions, but it is certainly something you should take advice on from a local solicitor. Ask them for a free initial meeting about it, take details of your father's estate.
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