I have a supermoto and have looked into this in great depth
 
 you do not need ANY lights at all,inc brake
 Any lights fitted must work (not just tapped up)
 you do NOT need a speedo
 You DO need a horn (or a £5 halfords pushbike horn)
 You DO need a rear reflector
 you MUST have a reg plate
 
 Anyone who tells you differnt inc mot inspectors, can ring the DVLA for clarifacation