Entry is only technically prohibited to some danger areas. Those to which it is are marked with an asterisk on the 1:500 chart and also (rather cryptically) with "SI" in the remarks section of the AIP document to which Getrude provided a link.
Thus, entry to 216 is not prohibited from what I can see. Good airmanship would dictate you try to stay out and/or you try to find out the status from London Information or some such, but if you can't and you creep just a little inside you're not actually breaking the letter of the law. Given that it's helicopter landing and parachute dropping it seems like a good lookout would serve you well.