The Inheritance (Provision for Family and Dependants) Act 1975 permits a spouse/cohabitee of the deceased, or a child of the deceased, or anyone who was wholly or partly maintained by the deceased and for whom inadequate provision is made by Will or the intestacy rules to apply to the court to make reasonable financial provision out of the estate.
This has therefore been a brake on the idea that you can leave your estate exactly as you wish. I understand that lawyers drafting wills advise on this in those cases where the client wants to leave everything to the donkey sanctuary.
The Court evaluates all the claims on the estate and tries to achieve an outcome that is fair to all.
Here is the judgment: http://www.bailii.org/cgi-bin/markup.cg ... od=boolean
. The case before the Court of Appeal was not about whether
provision should be made out of the mother's estate for the daughter but about the amount
of such provision. The charities still got something, quite a bit actually, but not everything.
In many other countries the law is more prescriptive and you have no option to disinherit.
the 1975 Act: http://www.legislation.gov.uk/ukpga/1975/63/contents