In 1973 the appearance of registration plates was changed for the first time since 1903. From 1 January, vehicles were required to have reflective number plates - black on white at the front and black on yellow at the back. Reflective plates were introduced so that unlit vehicles could be seen more easily at night. The regulations also provided for the size, shape and character of registration marks.
Therfore the law states its illegal to display your number plate as it is.
The consequences are as following if the police stop you.
1. they will do nothing andf let you go, (probably not happen)
2. you will receive a none endorsable fixed penalty £30
3. At best be issued with a VDRS (vehicle defect rectification scheme) ticket which allows you 14 days to rectify the plate, take t to an MOT centre and return the endored ticket resulting in no further action.
The choice is yours.