Hi,
For trials type bike MOT's the guide lines are as follows:,
lights not required (advisory will be issued warning presenter not to use bike in times of bad visibility)
Reflector not required.
Horn must be of a continious audiable note, (bikes reg before august 1973 a bulb type horn is acceptable)
Speedo not required,
Exhaust no longer requires E mark or bsau markings (but must not be noisy)
Number plates have letters on two lines,have a standard font ,black letters on yel ref backing and must be readable from approx 15mts.
(bikes reg before jan 1973 can have white letters on a black background)
Tyres must be E marked.
Seat must be secure (stick on or painted on seat pads acceptable)
all the other testable components follow the same guidelines of a standard road type motorcycle.
hope this helps.P..