First, your will must be valid. There are various rules that must be followed: it must be in writing, and executed in the right way. You have to sign it in the presence of two independent witnesses. But make sure the witnesses do not benefit under the will and are not married to someone who benefits.
Homemade wills are much more likely to fail than those made professionally.
Second, you must have the capacity to make a will. Capacity can be affected by poor health, physical and mental. If this is a factor then it is sensible to involve a doctor to certify that you do have sufficient capacity.
Third, you must make the will freely, not under the influence of someone else or under duress. The will won’t be invalid simply because, for example, someone pressured you to leave them a gift, by appealing to morality or pity. What’s required to invalidate a will is ‘coercion’.
The courts will declare a will invalid if the tests above are not met. However proving that there was undue influence on someone making a will, or that they lacked capacity, is not easy. Claims can be expensive, and anyone thinking of challenging a will should take legal advice before they start.
For more information on making a will click here. To find out more about challenging a will click here.