I contacted the Directorate of Airspace Policy at the CAA having been MORd for being 3 minutes late into a NFZ and their response was interesting. Firstly they felt that it was unsafe to fly in the area of high concentration although it was admitted unofficially that was only with respect to turbine aircraft and that nothing specific was being said for VFR SEP flights.
It was also made clear that there is NO legal basis for the "no fly zone" on purpose because while they thought it was important to stress the area of high concentration and that people flying in it should turn round and fly out but that people should not be prosecuted for doing so. They also said that it was an overreaction to withdraw all ATC service from people in the zone for whatever reason albeit by 3 minutes, but that was an understandable interpretation. If it was to be airspace then it would have been called so, that would make it legal
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On that basis not one person will be prosecuted for flying in a no fly zone. You may be MOR'd but it will get filed in the nonesense drawer.
The problem we're facing at the moment is that no consideration is being given to piston aircraft flying VFR, it makes little sense for us to be banned from flying unless there is a very clear danger and there isn't. How do we know this? Because regardless of the NFZ notams, people have been flying quite regularly and have not been dropping out the sky.
I've yet to find someone to talk to who will accept that VFR SEP/MEP flights should be permissable and that removing FISO/tower/air-ground services from those flights on the basis that we shouldn't be flying turbine aircraft is absurd and excessive.
Good luck AOPA! Hopefully you can knock some sense into NATS/CAA/Metoffice so they can at least let us fly our little put puts on these lovely days!