ModernDinosaur,
Just to the south of Biggin there's a set of tennis courts that is lit up by some very bright white lights (four, I think). Once you've found them, look west and you should see the perimeter road lit up by a line of orange lights. This runs roughly parallel to the runway, so if you look a little to the east of it you should be able to see the runway - though I agree, unless you're directly lined up with it on final approach it can be difficult to spot.