Perhaps unsurprisingly the newspaper article provides little detail about the legal arguments in this case. But it appears to be based upon the existence of a secret trust, which would not be advisable since they rely wholly upon the trustee to do what they are asked to do after the death. 

Mrs Titcombe stated that Mr Ison (the beneficiary in the will) was part of the video call where it was agreed. 

This was always going to be a difficult case to prove as it is classic "he says/she says". 

Nevertheless an interesting case.