In 2017 there was a 6% increase in the number of instances whereby people (often concerned family members or those who felt entitled to benefit from a Will but did not) made applications to attempt to block a grant of probate being obtained.

According to the article, the most common reason for entering a "caveat" (to temporarily halt the process of obtaining a grant of probate) is on the grounds of "undue influence". 

The burden of proof is on the person trying to argue that there was undue influence. They must show that there was coercion which caused the testator (the person who's will is being challenged) to do something that he / she did not intend. Persuasion alone may not necessarily amount to undue influence.

The next most common reason to enter a caveat is said to be on the grounds that the testator, lacked "testamentary capacity". 

One of the benefits of instructing a Solicitor to oversee the Will making process is that they will, as a matter of course, be assessing the testator's capacity. In the event that the Will is ever challenged on the ground that the testator lacked testamentary capacity, then the Court will have reference to any file notes, correspondence and observations that the solicitor obtained.