Hi Dan,
I recently completed the UK Tour.
I use Just Flights VFR Scenery (Payware) and that has Silverstone included but unfortunately it's not really the airport, just the Photoreal scenery. I flew a radial of 155 degrees from Daventry VOR to find the VFR scenery version and it is about 7.5 nm. The Coords roughly to the middle of the airfield are:
52:04:30N
1:00:35W
Sorry I couldn't be of further help.
Good luck,
Phil