Originally Posted by TomS
There's a specific letter height and amount of spacing between each character that it needs to be. It's not the size of the plate, it's the size of the characters and spacing between and around them.
If you go for an MOT without you're full-size plate they will fail you for it, I always keep mine in the boot just in case.
They won't fail you if they know the correct laws or you have the documentation with you. I've never had issues with cut down plates following the legal criteria. Think of the other end of the stick such as the older Jags and Rover 75's they had massive plates oversized to fill the back recess.
For example like my old Impreza here many years back, this passed MOT's no issues and the plate is much shorter.
My Supra which ran no front plate however didn't pass an MOT due to no plate