If you ever come up behind an old car on the M way in the dark,or poor visibility, the rear lights can be pitiful. If you break down on the M way, or a dark lane and can't keep the lights on, all you've got without reflective plates is the two small reflectors.
It's risky enough on the hard shoulder as it is. Reflective plates add a significant extra area of reflected light, and I would not fit black & silver plates for that reason alone.
It's a reason to get stopped, and it's a reason for your insurance company to argue the toss.
End of sermon!
