Joel,
Had exactly the same experience at Sleap in the past. Initially there was no real explanation for the questioning - I had to give my details along with those of my passenger. They then started to suggest it was do with potential customs violations, even though the flight had originated at Barton. I was just relieved it wasn't in relation to my dubious joining procedure at EGCV!
Guess it's proof that anything south of 53N is a twilight zone - my advice is get yourself back to the 'safety' (and sanity) of the north as soon as possible!
Simon