Can I bring a claim against an estate even if the Will has been validly made?

Yes.  The Inheritance (Provision for Family and Dependants Act) 1975 (more commonly known simply as the “1975 Act”)  allows certain categories of people to apply to the court for an order for what is known as “reasonable financial provision” in the event that they are either not provided for, or not provided for sufficiently, within a testator’s Will.