If you are reading this now, the answer is no.
Except if they were made and fitted before the 1st of September 2021. As of the 1st of September 2021 British Standard AU 145e came into effect, which heavily restricts how number plates can look.
The main changes to the previous British Standard AU 145d is that the use of textures, patterns or raising of the characters in anyway is no longer allowed, the characters must be made of a single colour. The British Number Plate Manufactures Associate detail the new requirements well.
Why? This change is to allow for ANPR cameras to read number plates further away, between 750,000 – 1.2 million number plates are misread every day by ANPR. To confirm this there is a new near infrared contrast test, and any number plate with textured or raised characters will fail this test.
Under British Standard AU 145d it is all ready a requirement that the whole character must be the same colour black. And as such, many 4D plates with a different backing or side colour are not legal. A number plate must not be treated in any way that makes the characters of the registration number any less readable by eye or that would prevent or impair making a photographic image of the plate. Treatments include the use of tints, films, coverings, or other coatings over the surface of the number plate.
Fines for having a non-legal number plate?
At the moment it is a non-endorsable offence, meaning you only get a fine. Which is currently £100. The chances of being caught is minimal, and to some the fine is minimal. As such, we see lots of people using non-legal number plates on the public roads.
BUT… it is currently going through Parliament for this to change under Bill 2794. This will include not having a BS AU 145e approved number plate, no number plate fixed to the vehicle and obscuring a number plate in some fashion.
With points ranging from 3 – 11 for not having a number plate fixed or having it obscured, and 1 – 6 for not having a BS AU 145e confirming number plate, but the endorsement is discretionary.