The airfield has never been freely avialable to visiting aircraft.
The process is, and has been for sometime, along these lines:
1) call up the police airfield manager, tell him you reason for visit
2) if reason acceptable (e.g. fly in for maintenance), and
3) you had a named sponsor (e.g. maint company manager)
4) provide you with an airfield briefing) and
5) sent a fax of insurance with £7.5m Crown Indemnity, to police
6) you get a logged PPR number, which is your permission to visit
Acceptable reasons are basically "business purpose visit to companies, clubs on the airfield".
Visiting businesses, even your own business, relatives etc in the area are not the type that cut an ice. Other govt MOD/RN/RAF aerodromes support a policy of enabling civilian use - the majjority of MOD/RN/RAF airfield are less restricted than Lee in this regard.
Where did Polly Vacher get to on her charity tour this year? Where not? Why not? Lee is not in the flight guides. and even if it were, it is unlikely that permission would have been granted to include Lee in the UK tour. I may be wrong on that, so if someone is proposing a charity flight they should still ask.