Anyone who is likely to benefit from an earlier will or on intestacy (where there is no earlier will) is able to contest a will.
If property is given away in a will, which was either gifted or promised to you during that person’s lifetime, you may also be able to challenge this.
If you’ve been left out of a will or didn’t inherit as much as you had expected then you may also be eligible to bring a claim for financial provision under the Inheritance (Provision for Family and Dependants) Act 1975.