The controlled low level airspace of a weapons range at 3am could conceivably be regarded as a relatively safe bet without a NOTAM though, maybe? But why not NOTAM it? Don't see the need to keep it secret really, unless they're doing something they don't really want us to know about I suppose. But what could be so secret about using a UAV over the land in the UK, other than flying it around? Can't imagine it'd be anything too exciting.
The wind farm lies slap bang on the 'commute' from Donna to Waddington. Bang on it. It's intriguing, but just an observation.
For the record, the delta Raven looks a hell of a lot like what we saw.