My father died, and transferring his mileage was easy, and free (less the cost of postage). I had to send them an original copy of a death certificate, and a signed form which is available on their website.

They wanted the form signed and stamped by a notary, which I didn't get stamped do the first time, and they demanded that it was stamped. They had already received the death certificate in the post, so they allowed me to fax in a copy after it was stamped.