Why the theory that Britain turned Canaris is hard to sustain

Could British intelligence have turned Canaris during his 1915 visit to Plymouth?

It is unlikely because the visit was brief, Canaris had little immediate value, and Britain would have faced major difficulties controlling him after his return to Germany.

A viewer asks whether Canaris could have been arrested and recruited by Britain during his First World War movements. The available time was extremely short, Canaris had little immediate intelligence value, and a public capture may have offered Britain more than a risky recruitment. British intelligence would also have faced the practical problem of controlling him once he returned to Germany. Testing the theory against opportunity, value, and agent handling makes it less persuasive than the mystery of Canaris's later career might suggest.