The 2001 rules are here:

Rules

And a good explanation here:

Speed Traps

They don't say exactly where, but the number plate has to be clear and legible. I suspect that "under the bumper" would be considered too low to be clearly legible.

Today the issue is more about ANPR Camera reading than Mr Plod.

Last edited by Aldermog; 12/08/14 08:00 AM.
Peter,
66, 2016 Porsche Boxster S
No longer driving Tarka, the 2014 Plus 8...