Child car seat laws in the UK: Which? advice

Using a child car seat is a legal requirement in the UK, but the rules can be confusing. Here's all you need to know so you don't get pulled over and fined.

We'll cover everything from UK car seat laws, and the differences between height and weight-based car seats, to whether you can use them in a taxi, minicab or Uber.

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What is the law for child car seats?

UK law states that children must use a car seat until they're 12 years old or 135cm/4ft 5in tall, whichever comes first.

However, safety experts, including Which?, recommend that you use a child car seat for all children under 150cm/4ft 11in. This is the legal requirement in Ireland and some other European countries, such as Germany and Poland.

For children weighing more than 36kg (5st 10lb) but under 150cm/4ft 11in, our advice is to go by height – so wait until your child is 150cm before letting them use the vehicle seatbelt. 

Only an EU-approved car seat can be used in the UK. Those approved outside of the EU can't be used in the UK, and EU-approved seats can't be used in other countries, such as the US.

Buying the wrong one could mean you're putting your child's life at risk, while also breaking the law. 

Which? crash tests all models we review, so we only recommend the best child car seats 

What is the correct child car seat?

You need a child car seat that:

• conforms to the United Nations standard, R129 (i-Size is a part of R129) or ECE Regulation 44/03 or ECE 44/04 (this is marked on a label on the seat)
• is suitable for the child's weight and size, or height (if buying an i-Size seat)
• is correctly fitted according to the manufacturer's instructions.

Don't get caught out using a booster seat incorrectly. Read our guide: Car seats for older children: high-back vs backless booster seats

Height-based or weight-based car seats?

You can choose one based on your child's height or weight.

Height-based car seats

i-Size is part of the European child car seat regulation R129, which was introduced in the UK in July 2013.

i-Size car seats go by height instead of weight. A true i-Size car seat will only use Isofix connectors, although some baby car seats can still be installed using the car's adult seatbelt. It's mandatory for a baby to be rear-facing in an i-Size seat until they are 15 months old.

i-Size car seats will fit all i-Size-certified cars and almost all vehicles with Isofix. Check with the car manufacturer to see in which position you can use one.

Weight-based child car seats

Other child car seats are split into groups according to the weight of the child.

These groups are defined by United Nations safety regulations R44/04 and cover children from birth up to 12 years old or 135cm (around 36kg). 

Moving babies and younger children up to the next group before they reach the maximum weight or height for their seat could lead to more severe injuries in the event of a crash. It’s also against the law to put your child in a seat that’s inappropriate.

See car seat weight and height groups to understand which group is best for your child.

When can a child sit forward-facing in a R129 car seat?

By law, your child must sit rear-facing in a car seat until they are 15 months old.

Extended rear-facing car seats are quite common now. Crash tests show they're safer, plus they keep your child rear-facing until the age of four – which we think is preferable. 

We explain everything you need to know in our guide to extended rear-facing baby car seats.

Child car seat law by age

Here are the laws for child car seats by age. Note that the rules for vans are the same as for cars.

Child up to three years old

• Who is responsible? The driver
• Front seat Correct child car seat must be used based on their weight or height (see above).
• Rear seat Children under the age of three must be in a car seat. If there’s no room for a third seat in the back of your vehicle, children aged three or under can use the front passenger seat, but only if they're in a child car seat. If your vehicle doesn't have seat belts in the back, a child under the age of three can’t travel.

You can’t take children under three years on an unexpected journey over a short distance in a vehicle without a seatbelt or the correct child car seat. The only exception to this rule is if it's in a licensed taxi or minicab (private hire vehicles) and the child travels on the rear seats.

See the best baby and child car seats that came out top in our crash tests.

Child from third birthday up to 135cm in height, or 12th birthday, whichever they reach first

• Who is responsible? The driver.
• Front seat Correct child restraint must be used based on their weight or height (see above). 
• Rear seat If there’s no room for a third child seat in the back of your vehicle, children aged three or older can sit in the back using an adult belt.

If your vehicle doesn't have seatbelts in the rear, a child aged three or older can travel in the back seat without a car seat and without a seatbelt. This rule only applies if the car came without seatbelts in the back originally. A child aged three or over can travel in the rear seat of a licensed taxi or mini cab (private hire vehicle) without a car seat, but only if they wear an adult seatbelt. For journeys that are unexpected, necessary and over a short distance, a child aged three or over can sit in the back only, using the adult seatbelt.

Child aged 12 to 13 years old, or younger and taller than 135cm

• Who is responsible? The driver.
• Front seat: Seatbelt must be worn.
• Rear seat: Seatbelt must be worn.

Passengers aged 14 years old and over

• Who is responsible? The passenger.
• Front seat: Seatbelt must be worn.
• Rear seat: Seatbelt must be worn.

Children with disabilities or medical conditions

Gov.uk states that the same rules apply for children with disabilities or medical conditions, but they can use a disabled person’s seatbelt or a child restraint designed for their needs.

A doctor can issue an exemption certificate if a child is unable to use a restraint or seatbelt because of their condition.

Do you need a child car seat in a taxi, minicab or Uber?

A driver can be fined up to £500 if a child under 14 isn't in the correct car seat or wearing a seatbelt while you're driving. However, there are exceptions to the law when travelling in taxis, minicabs and Ubers.

• Children under the age of three can travel without a child’s car seat or seatbelt, but only on a rear seat.
• Children aged three or older can travel in a rear seat without a child’s car seat if they wear an adult seatbelt.
• A 2022 Which? survey* by found that 52% of parents thought you could be fined if you don't use a car seat for your child in a taxi.

If you have a child under the age of three, some experts feel the best option is to sit the child next to you on their own seat (if they're able to) or use your own car seat.

Holding them on your lap isn’t the best idea, because in the event of a serious crash your body weight may crush the child or, even worse, they may be flung out of the car.

We would recommend finding a taxi firm that can provide a car seat for when you travel, or bring your own. 

_{*Survey carried out in February 2022 of 2,004 parents with a child under the age of five.}

Do minibus or coach firms need to provide child car seats?

Minibus or coach drivers and companies don’t have to provide child car seats, so you'll need to bring your own.

On coaches, there's no law requiring children to travel in a child car seat or to use a seat belt, if they're not available.

For minibuses, all children need to travel in rear seats (behind the driver) if a car seat or adult seat belt is unavailable. Children aged three or older must use a car seat if there's one available. If there isn't a car seat, they must use an adult seat belt.

Shopping for the perfect seat for your little one? Check in with our expert child car seat reviews

Other exceptions to the child car seat law

No room for a third child seat in the back

If there’s no room for a third child seat in the back seat (where two occupied child car seats in the rear prevent the fitting of a third one) a third child under the age of three can’t travel unless they're in the front seat with the correct child seat.

Children aged three or older can either use the front seat with the correct seat or sit in the back using an adult belt.

Unexpected, but necessary, journeys over a short distance

If you need to make an unexpected but necessary journey and you don't have the correct car seat, a child over three years old can use the adult seatbelt. 

You must not take children under three in a vehicle without a seatbelt or the correct child car seat (except in the back seat of a taxi or minicab).

Vehicles without seat belts

The following rules only apply if the vehicle was originally made without seatbelts.

Gov.uk states that children under three must be in a child car seat. If there’s no seatbelt, they can’t travel. A child aged three or older can travel in a back seat without a car seat and without a seatbelt if the vehicle doesn’t have one.

Penalties for ignoring the law on using child car seats

The consequences of ignoring the legal requirements could be expensive (at best) and (at worst) fatal. Police are able to administer an on-the-spot fine, which could be as much as £500 if the case is referred to court.

Remember, the driver of the vehicle is responsible for ensuring all passengers are safely strapped in. 

Thankfully, it seems parents are becoming increasingly clued up on what you'll be fined for when transporting children. A 2021 Which? survey* found that 88% of parents know they can be fined if they don't use a car seat for their own young children, while 86% of parents are aware of the law stating they can be fined for not using a seat for someone else's young children.

_{*Survey carried out in February 2021 of 2,021 parents with a child under the age of five.}

Why can't children just use an adult seatbelt?

Children need their own specially designed child car seat to keep them safe in a crash because their bodies are not simply smaller versions of adult bodies. 

As babies' bodies are in the early stages of development, they need protection based on specific physical traits:

• Different proportions – babies have bigger heads and smaller limbs.
• Babies' major organs are in different places.
• Babies' bones and muscles aren't fully formed.
• Babies are more vulnerable to injury than adults.

Car seats are designed to protect a child's most vulnerable areas at each stage of their development.

Restraint systems – adult seatbelts and car seats – are designed to do three things:

1. Keep people away from the vehicle structure during a crash.
2. Reduce their momentum in a controlled way.
3. Distribute the forces of a crash over the strongest parts of the body, with minimum damage to the soft tissue and organs.

Children are too small to position the adult belt over their shoulders and pelvis correctly, and their bones aren't strong enough to absorb the energy of a crash without affecting their internal organs.

A proper child-restraint system provides the best protection for kids as they change and grow.

Follow our expert tips to install your car seat and check the fit effectively – see our guide on how to fit a baby or child car seat

Can I use a carrycot instead of a child car seat?

Our experts agree that the safest way to transport babies is in a rearward-facing infant car seat. A good one will help protect your baby in both frontal and side-impact crashes.

However, carrycots can be a good solution for newborn babies, especially premature babies or those with medical conditions who need to be transported lying completely flat.

In this instance, we'd recommend a car seat carrycot with good crash test results.

However, they take up a lot of space on the back seat, which may not be practical if you have other children. They also tend to be outgrown more quickly than standard baby car seats.

A pushchair carrycot should never be used in a car, unless it's approved for use as a child car seat.