But what about ex Mil with loads more aerobatic experience than me?
Once holding a part-FCL FI certificate and an Aerobatic Rating, they will be able to conduct aerobatic instruction after demonstrating ability to a suitable FIC instructor in accordance with CAP804 Section 4 Part J, Subpart 1 Page 1.
Between now and 17 Sep there is something of an interregnum, so any military pilot who has added an FI certificate under the niggardly MAS would be best advised to wait until then before applying.