Quick question Dave, don't know if you know the answer to this but something
  I was looking into but never found the result.
  As stated you buy the van for £15,000, depreciation 3yrs x £1,500 = £4500
  You sell the van after 3 yrs for £9,000 so £6,000 difference from when you
  first bought the van. Have only claimed £4,500 depreciation so could you
  claim for the difference between £6,000 and £4,500.
  I know if the depreciation value of your van in your accounts was lower 
  than your selling price you would have to add this as profit on your
  accounts.
  Hope this makes sense.
 Doug