Not legal, apparently though I suppose some take the risk and get away with it.I wonder if it is legal to put a transfer type plate on the bonnet, and if so how it would look. See to recall car such as E type jags often had such in the past.
Fixing of registration plates: vehicles registered before the relevant date
7. - (1) This regulation applies to vehicles, other than works trucks, road rollers and agricultural machines, first registered before the relevant date.
(2) Except as provided in paragraph (4), a registration plate must be fixed in the manner required by paragraph (3) on -
(a) the front of the vehicle, and
(b) the rear of -
(i) the vehicle or,
(ii) where the vehicle is towing a trailer, the trailer or,
(iii) where the vehicle is towing more than one trailer, the rearmost trailer.
(3) This paragraph requires each plate to be fixed -
(a) in a vertical position or, where that is not possible, in a position as close to the vertical as is reasonably practicable, and
(b) in such a position that in normal daylight the characters of the registration mark are easily distinguishable, in the case of a plate fixed on the front of the vehicle, from in front of the vehicle and, in the case of a plate fixed on the rear of the vehicle or trailer, from behind the vehicle or trailer.