Front sticky is a no no. If you left the original plate with the holder on you would be fine as the DVLA states. He cant fail you on the rear plate because a plate with British sized lettering does not fit in the recess. But since you took the holder off you have a whole front bumper to fit a British sized plate. I fell into this trap when i was stopped by the police in Aberdeen.
I copied this from the site, it might help.
The Road Vehicles ( Display of Registration Marks) (Amendment) regulations 2002 SI no. 2687 came into force in November 2002.
These amendment regulations introduce a new regulation 14A, making special provision in relation to the size and spacing of characters in the registration number of some imported vehicles. These regulations also include the display of motorcycle sizes for number plates on imported vehicles. The provision only applies to vehicles imported into the UK which do not have European Community Whole Vehicle Type Approval, and are so constructed, that the area available for the fixing of the registration plate precludes the display on the plate of a registration number in conformity with the requirements of regulation 14.
Also contained is an amendment to regulation 3, to prohibit the use of a number plate on which the background is patterned or textured, or gives that appearance.
Where a vehicle has been allocated a UK registration number, the number plate must comply with the specification and standards laid out in the Road Vehicles (Display of Registration Marks) Regulations 2001, as amended. Certain imported vehicles may be permitted to display numberplates with smaller characters if the vehicle does not have European Community Vehicle Type Approval and the vehicle's construction/design cannot accommodate standard size numberplates.
The dimensions for the smaller sized plate are:
• each character in the registration number must be 64mm high
the width of each character of the number, other than the letter 'I' and the figure '1' must be 44mm
• the width of every part of the stroke forming a character in a number must be 10mm
the spacing between any two characters within a group must be 10mm
• the vertical spacing between groups of characters must be 5mm
• the width of a margin between the number and the top and lateral sides of the numberplate must be not less than 5mm
• the space between the bottom of the number/character and the bottom of the plate must not be less than 13mm, but within that space, the space between the bottom of the number and the top of the name and postcode of the person the plate was supplied must not be less than 5mm.
