HD
When I retired I was given to understand that senior officers (Sqn Ldr and above) and their equivalents in the other services could use their rank if they wished. Junior officers could do so, but only after obtaining permission. Presumably Captain Mark Philipps got the ok! I've never bothered and after 18 years I cringe if someone raises the subject - Mr seems fine to me, but sometimes it may be relevant to the job someone's doing, so horses for courses.