The instructor then got a letter from PLD telling him to stop instructing.
Before any such action could be taken the person concerned would be invited for interview to be conducted by two pilots; the interviewee may take a friend or representative or, may decline the invitation. Unless there is a major safety issue, the above action is most unlikely. The CAA will only revoke a licence or rating if the holder is deemed an unsuitable person to hold the licence or rating; in most cases that would be the result of a court conviction.