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