Aerodrome Licence
WBS,
It depends on the Aerodrome Licence. If it is a Public Use licence then the aerodrome has to be available during its published opening hours (although there are exceptions.) If it has an Ordinary Licence, and I suspect Sywell has, then the licensee can more or less do as they like as the airfield is only licenced for use by the licencee 'and by persons specifically authorised by him.'
See Chapter one of CAP168, also available on the CAA web site.
If anyone is so inclined it might be worth a call to Aerodrome Standards at Gatwick.