I have not participated in the trial since it's very unlikely I'll be flying anywhere near London those days, but I was just wondering. What if I use homebriefing.nl or use the Dutch FIS telephone number to file an (international) VFR flight plan which does cross the restricted area, but does not *exactly* conform to the special rules for these plans?
Most likely it will be accepted by the Dutch FIS because it conforms to the international/ICAO rules for FPLs, so I get an acceptance message. The plan is then forwarded to the UK authorities (which ones I honestly don't know - normally only the destination is informed). And they can't do anything with it because it doesn't conform to their special ruleset. What happens then?