Of course it's an illegal regulation - I wouldn't mind betting that it's an admin matter that it exists in the AP; it'll probably be changed when the next amendment is issued.
These APs are routinely reviewed and amended at varying intervals; the interval depends on many factors, including the rate at which the subject matter is likely to change. For example, computer security regs will be reviewed and changed much more frequently to keep abreast of the latest innovations in technology. By contrast, parade ground regs are usually set in tablets of stone and amended by clerks using quills - there is little need to change the way parades are conducted.
Besides, readership numbers are probably very low, and neither is it likely to be challenged in court [not worth the effort, unless you are a rabid anti-discrimination type].
A call to the appropriate office in MOD will probably bring a signal amendment out within a few days...