I think you are right that it only has to be legible (along with engine and frame numbers) for MOT purposes.
However I suspect it is left fairly open to the testers discretion what 'legible' actually means, and you'd have no grounds for argument if they decided to say "this plate doesn't conform to standard, therefore I can't read it, therefore i'm failing it." You can't exactly go running to VOSA and complain that "the nasty MOT man wouldn't give me an MOT with my illegal reg plate". Depends where you go and whether the tester got any last night
![:smt002](./images/smilies/002.gif)
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It's probably all academic really given a) it'll be a free retest item; and b) it takes a couple of minutes to swap. So you could either try it and have to go back if it gets failed, or just change it for the MOT every year and run the (slim) risk of getting pulled the rest of the time
In the garage:
Kawasaki ZXR400 L3 - shiny
Suzuki DR800 - bouncy
1978 Suzuki GS400 -
PROJECT RETRO RACER!
Kawasaki GPz500S - for sale soon
Honda CG125 BR-J - in bits