It may set a precedent. I recognise that there is a potential security issue although HM is not a permanent resident of the West Slough area. Windsor Great Park is, I beieve, already on the Royal Parks list of no palaces to fly (if only there were an easy, free and up-to-the minute app to check on where flying is allowed …). Why not have a restricted area activated by NOTAM only when HM is at the castle?
There are many residences for members of the House of Windsor around the country - will granting this restriction open the doors to permanent FRZs around each and every building? And will eevry person and organisation that thinks UAVs may be one way of causing them harm be able to apply for a FRZ?
The problem is that, to the non pilot, this is an eminently sensible and probably necessary measure to further ensure the security of our (beloved) monarch.