What Makes a Number Plate Road Legal in the UK?
When replacing your number plates, it can be tempting to choose a style based purely on how it looks. But if you’re going to use your plates on public roads, they need to meet specific legal requirements.
So, what makes a number plate road legal in the UK?
From the materials used and the colour of the plate to the character size, spacing and markings, there are several requirements that need to be met.
In this guide, we’ll explain the main UK number plate requirements, what BS AU 145e means, and what documents you’ll need when ordering a road-legal set.
What are the legal requirements for number plates in the UK?
For vehicles first registered on or after 1 September 2021, and for replacement plates supplied for vehicles first registered on or after that date, the plates must meet the relevant requirements of BS AU 145e. Plates for older vehicles may be subject to the earlier BS AU 145d standard, depending on when they were manufactured and supplied.
In simple terms, a road-legal number plate must:
- Be made from compliant retroreflective material.
- Have black characters on a white background at the front.
- Have black characters on a yellow background at the rear.
- Display the registration correctly.
- Use the prescribed character style, size and spacing.
- Not have a background pattern or other feature that interferes with the registration.
- Have the required British Standard and supplier markings.
- Use characters that are not reflective or removable.
- Use a single shade of black for the characters on plates subject to the BS AU 145e requirements.
The rules are designed to make registration numbers easy to read and suitable for systems such as ANPR cameras.
What does BS AU 145e mean?
BS AU 145e is the British Standard specification for number plates manufactured under the current requirements.
It covers the characteristics and performance of the plate, including its construction, visibility, strength and reflectivity.
For plates subject to the current requirements, BS AU 145e is the relevant British Standard marking.
You’ll normally find the BS AU 145e marking discreetly positioned underneath the registration characters, although its exact position can vary provided it meets the applicable requirements.
This is one reason it’s important to buy road-legal number plates from a registered number plate supplier, rather than simply purchasing a plate from an unregulated source.
What colour should a legal number plate be?
For standard vehicles, the requirements are straightforward:
Front: black characters on a white background.
Rear: black characters on a yellow background.
The plate material must also be retroreflective.
A decorative or tinted appearance doesn’t override these requirements. If a plate doesn’t meet the required specification, it shouldn’t be used as a road-legal registration plate.
Do number plates have to use a particular font?
Yes.
UK registration plates have prescribed requirements for the appearance, size and spacing of their characters.
For modern vehicles, the characters must use the prescribed Charles Wright font and meet the relevant dimensions and spacing requirements. Characters must not be designed in a way that makes one registration character look like another.
For example, characters must not be italic, sloping or formed using broken or multiple strokes.
The standard character height for most modern vehicles is 79mm, with specific exceptions for motorcycles and certain other vehicles.
This is important when choosing a shortened or customised plate. The plate itself can be made to different overall dimensions, but the registration still needs to be displayed in the legally required format.
Can a road-legal number plate have raised characters?
Yes.
Raised or 3D characters are permitted on number plates, provided the finished plate complies with the relevant requirements.
For plates subject to the BS AU 145e requirements, the characters must be a single shade of black, including the sides of raised characters.
This means that the fact a plate has raised characters does not automatically make it illegal. It’s the specification of the finished plate that matters.
If you’re specifically comparing different raised-character styles, we’ve covered that separately in our guide to 4D vs 3D gel number plates.
What markings must appear on a legal number plate?
Modern road-legal number plates have more than just the registration number printed on them.
Under the current requirements, plates must display markings identifying:
- The relevant British Standard, such as BS AU 145e.
- The manufacturer or supplier of the components used to assemble the plate.
- The suppliers name and postcode.
These markings have prescribed requirements and must not interfere with the visibility of the registration.
These details allow a plate to be linked back to the supplier that produced it.
Can I have a border on my number plate?
A border can be permitted, provided it meets the relevant requirements.
For modern plates, an integral raised or depressed border around the periphery can be used within the prescribed limits.
The border must not interfere with the registration characters or required markings.
If you’re looking for the cleanest possible appearance, a plate can also be produced without a border.
Can I have a shortened number plate?
A shortened number plate can be possible, but there isn’t one universal “legal minimum size” that applies to every registration.
What matters is whether the registration can be displayed while still meeting the required character dimensions, spacing and margins.
This is why two registrations containing the same number of characters can sometimes require different overall plate dimensions.
There are also specific rules for motorcycles and certain imported vehicles where the available mounting area can affect the permitted character dimensions.
If you’re considering a short plate, don’t simply choose the smallest plate that looks good on the vehicle. The registration needs to remain compliant when displayed on the finished plate.
What documents do I need to order road-legal number plates?
This is an important part of buying number plates legally.
A registered number plate supplier must check that you’re entitled to use the registration you’re ordering.
For road-legal orders, you’ll need to provide:
- Valid proof of identity, such as a driving licence or passport.
- Proof that you’re entitled to use the registration, such as a V5C, green new keeper slip, V750, V778 or other accepted document.
Once your documents have been checked, we can make your plates to the specification you’ve selected, provided that the selected design and dimensions comply with the applicable requirements.
I’ve just bought a car — can I still order plates?
Yes, you may be able to.
If you’ve recently bought a vehicle and haven’t received the V5C yet, the green new keeper slip can be used as proof that you’re entitled to display the registration, where applicable.
You’ll still need suitable identification when ordering.
If you’re unsure which documents are appropriate for your circumstances, it’s best to check with us before placing your order.
What if I’m using a private registration?
If you’ve purchased or retained a personalised registration, you’ll need the appropriate documentation showing your entitlement to that registration.
For example, a V750 Certificate of Entitlement can be used to prove entitlement to a number that has been purchased, while a V778 Retention Document can be used in relevant circumstances.
Once you have the appropriate documentation, we can manufacture the physical plates for you.
Remember, buying a registration number and buying the physical number plates are two different things.
Why do I need to provide ID when buying number plates?
The documentation requirements aren’t simply a preference ours.
Registered number plate suppliers have legal obligations to check that customers are entitled to use the registration they’re ordering.
This helps prevent registration numbers being supplied to people who aren’t authorised to use them and provides a record of who supplied the plates.
So if you’re asked to provide ID and registration documents when ordering road-legal plates, that’s a normal part of the process.
What happens if my number plates aren’t legal?
Displaying a registration incorrectly can have more serious consequences than simply having an unattractive or non-standard plate.
You could be fined up to £1,000, and your vehicle can fail its MOT because of incorrectly displayed number plates.
It’s therefore worth checking the specification before ordering rather than assuming that any plate advertised online as a “number plate” is suitable for road use.
Road legal doesn’t have to mean boring
Complying with the regulations doesn’t mean you’re restricted to a completely standard-looking plate.
Depending on your vehicle and registration, you can choose from different compliant styles and specifications, including:
- Standard 2D characters
- 3D gel characters
- 4D characters
- 4D gel characters
- Different legal layouts and plate dimensions
- Shorter plates where the registration and vehicle allow
The important thing is that the finished plate remains compliant.
If you’re interested specifically in the difference between 3D gel and 4D plates, see our dedicated 4D vs 3D Gel Number Plates guide.
We’ve also explained the specific requirements surrounding whether 4D number plates are legal in our dedicated guide.
Order road-legal number plates from Plate Source
At Plate Source, we make number plates with the aim of combining a clean, premium appearance with the requirements for legal road use.
Whether you’re replacing damaged plates, fitting a personalised registration or simply upgrading the look of your vehicle, we offer a range of styles and finishes to choose from.
For road-legal orders, you’ll need to provide the relevant documentation confirming your identity and your entitlement to use the registration.
Once your documents have been checked, your plates can be made to the specification you’ve selected, provided the finished design meets the applicable requirements.
Quality plates. Straight from the source.