Quite interesting this...I did the bike ones - got one wrong on the first set (when the road sign piccy didnt display and I had to guess - LOL) and FOUR wrong in the second batch - time to brush up I think 
 http://www.dsa.gov.uk/
  http://www.dsa.gov.uk/  Click on "Mock Theory Tests" 
 also  
http://www.highwaycode.gov.uk/00.shtml  if you need to cheat 
