Is It Illegal to Undertake on a Motorway? (UK Guide 2025)
Undertaking in UK is not illegal in itself, but it’s strongly discouraged by the Highway Code and is illegal in most situations. Simply put, while you can pass a slower vehicle on the left in very specific circumstances, doing so is often considered reckless or unsafe driving.
Instructors at Ipassing Smiles help trainees to understand the meaning of Undertaking. Although it is not strictly prohibited, it is generally considered dangerous and can result in a fine if done irresponsibly.
In this guide, we’ll explain when undertaking is allowed, when it’s considered illegal, and what the Highway Code actually says about it. You’ll also learn about the penalties for reckless overtaking and a few safety tips for managing traffic properly.
What Does ‘Undertaking’ Mean?
Undertaking means passing another vehicle on the left-hand (nearside) lane instead of the right. In the UK, where we drive on the left, overtaking happens on the right (offside), while undertaking is overtaking on the left, something the Highway Code strongly discourages.
According to Rules 267–268 of the Highway Code, drivers should only overtake on the right. However, in slow or congested motorway traffic, you may keep up with vehicles in your lane even if it means passing cars on your right. Outside of these conditions, undertaking on multi-lane roads can be unsafe and may count as careless driving.
Is Undertaking Illegal?
Yes, in most cases it’s illegal, but there are limited exceptions. The Highway Code (Rule 268) states that you should not overtake on the left or move to a lane on your left to overtake.
However, it makes an exception for slow or congested traffic, where lanes move at similar speeds and the left lane happens to move faster. Outside these conditions, undertaking can be treated as careless driving under UK traffic laws, which may lead to penalties or fines for unsafe overtaking.
Is Undertaking Illegal in the UK?
In the UK, undertaking isn’t outright prohibited, but it’s strongly discouraged under the Highway Code. The distinction is important: while not always illegal, it can still lead to a fixed penalty notice if done carelessly or without due attention.
Police can treat an unsafe undertaking as careless driving under UK road laws, which may result in three penalty points on your license and a £100 fine. In short, it’s safer—and legally wiser—to overtake on the right unless traffic conditions clearly make left-side passing acceptable.
Is It Illegal to Undertake on a Motorway?
Yes, undertaking on a motorway is generally illegal and unsafe, except in limited cases such as slow-moving or congested traffic. The Highway Code clearly states that drivers should always overtake on the right-hand lane and maintain proper lane discipline.
Passing on the left at high speeds can confuse other drivers who may be moving back into the left lane, leading to serious accidents. This risk increases around middle-lane hoggers or in average speed check zones, where sudden lane changes are common.
If caught undertaking recklessly, you could face a £100 fine, three penalty points, or even harsher penalties for careless driving under motorway regulations.
Undertaking on a motorway in the UK is considered illegal in most situations. Unlike countries such as the US, where passing on either side is common, UK driving standards require drivers to overtake on the right and keep left unless overtaking.
Because UK motorways have more junctions, exits, and merging lanes, undertaking poses a greater road safety risk. Drivers may not expect to be passed on the left, which increases the chance of sudden collisions. To stay compliant with UK overtaking laws, always overtake safely on the right and avoid using the left lane to gain speed or skip queues.
Why Is Undertaking Illegal?
Undertaking is illegal mainly because it increases the risk of collisions and blind-spot accidents. Most drivers don’t expect to be passed on the left, so sudden lane changes or lack of awareness can lead to dangerous side impacts.
The Highway Code treats unsafe undertaking as careless or dangerous driving, especially on fast-moving roads. It reduces safe driving distance and limits a driver’s ability to react in time. To stay safe, always overtake on the right and keep a clear awareness of vehicles around you.
When Is It Acceptable to Undertake?
You should only do this in specific, low-risk situations. The Highway Code (Rule 268) allows this when traffic is moving slowly or is congested, and the left-hand lane is moving faster than the right-hand lane. In this case, you can stay in your lane rather than merging in and out.
It is also acceptable if the vehicle ahead is turning right, or when driving at average speeds or in “stay in lane” zones, where all traffic must stay in their lane. Outside of these scenarios, undertaking disrupts the normal flow of the motorway and can lead to a fine for careless driving.
Tip: Don’t use undertaking to pass middle-lane hoggers — it’s still considered unsafe. Wait until you can overtake on the right instead.
What Happens If You’re Caught Undertaking?
If you’re caught undertaking dangerously, police can classify it as driving without due care and attention — also known as careless driving. The usual penalty is a £100 fine and three points on your license, but serious cases can lead to larger fines or even a court summons.
Officers decide on a charge based on how reckless the behavior was and whether it poses a risk to other drivers. Safe, patient lane discipline is always the better option — it keeps you compliant with UK driving laws and helps you avoid unnecessary fines.
Q1. Is undertaking a serious fault on a driving test?
Yes. It’s usually marked as a serious fault because it shows poor lane discipline and disregard for the Highway Code.
Q2. Can you get points for undertaking on a motorway?
Yes. Careless or unsafe undertaking can lead to three penalty points and a £100 fine.
Q3. Is undertaking more common in heavy traffic?
Yes. It’s most common in slow or congested traffic, where the left lane moves faster than the right.
Q4. What’s the difference between a careless and a dangerous undertaking?
Careless means poor attention or judgment. Dangerous means creating real risk — like weaving at speed or cutting in.
Q5. Is undertaking ever legal in the UK?
Yes, but only in limited cases such as slow traffic, a vehicle turning right, or “stay-in-lane” motorway zones.
