My newly acquired TTR will be going in for an MoT test next week, but I have one question. The original number plate assembly (regular size plate, reflecter, number plate light) has been replaced by a slightly smaller number plate, with no number plate light and no reflector (it has a red rear light still of course).
One thing I am (fairly) sure of is that you need a reflector. Get one of those cheap stick on round ones and put it on a corner of the number plate. The MOT garage will probably sell them.
I tend not to take chances on MOTs and, if a TTR has had its rear number plate holder and rear light removed, I make sure that it has it replaced. Not worth taking a chance of having to take the bike home to do repairs and then take it back for a re-MOT.