Mike,
For a PA28 we're paying £714 + VAT PA for 'airfield use' i.e. a landing card. Parking on the grass is £1072 + VAT PA, totalling £1786. This is for a licenced aerodrome just inside the M25. We also have a/g radio. The only benefit of a licenced aerodrome for us is the ability to do ab initio instruction. Try enquiring specifically about keeping and operating an aircraft at White Waltham, I think they're about as expensive as it gets and probably still considerably under your Chief Constable's figure.
I've no doubt he took the cost of operating the aerodrome and divided that by the number of people he thought might use it. A bit simplistic!
Keep up the good work, i'm still looking forward to finally being able to fly in.
TheOddOne