Just so happened that at LHR on my way out to Germany last week, I bought a copy of Today's Pilot (which is not my normal mag, but thought I'd check it out!).
In this, there was a discussion on the current CAA position re: ejector seats. I don't have the magazine with me today, so I'm talking from possibly faulty memory here.
Essentially, I believe the CAA haven't really come out with any firm regulation regarding the fitting (and to some extent, more importantly, the maintenance and certification) of bang seats. It seems to be generally accepted that in Hunters, they are a 'good idea' but not mandatory. For lower performance aircraft, such as the JP, there seems to be a move towards mandatory removal of the seats, on the basis that use / maintenance of them by improperly trained personnel could reduce rather than increase personal safety. However, reading between the lines, there appears to be a degree of 'fence sitting' as a firm decision either way leads someone in the CAA liable to answer a lot of awkward questions if a positive policy is established and someone comes to grief as a result.
Fitment of seats in a JP is certainly not manadatory at the moment as I understand the article, however, IMHO it is a jolly good idea for personnel who are likely to be able to use them correctly and if they are to be correctly serviced.