Millions of drivers do not know about a small but potentially lifesaving button in their car, highways chiefs are warning.

National Highways says more than five million new cars are equipped with an emergency eCall system and SOS button – but many motorists don't know about it or even how to use it.

Four years ago, new legislation meant all new types of car and van must have the emergency call system known as eCall – which includes an SOS button – fitted in the vehicle.

In the event of a serious incident, it triggers the vehicle's airbags, sensors can activate the eCall system, which automatically sends the vehicle’s location to a 999 operator.

The system also enables drivers to speak with emergency call handlers.

Having precise co-ordinates for the accident and the car's whereabouts enables operators to direct emergency services to the vehicle, meaning help and medical care can also get there quicker.

The emergency safety feature can also be manually activated by those in the car, who can press the eCall system’s SOS button connecting them directly to emergency services.

Operators would also automatically receive the vehicle's details and through the speaker system can collect more information from those inside.

An SOS button provides, says National Highways, a valuable alternative to using a mobile phone if the occupants of the car don't have a phone, can't reach it or have the hands-free technology to use it depending on the circumstances.

Alongside medical emergencies, the system is designed to summon help if motorists can see someone else needs emergency assistance, such as a broken down vehicle blocking a lane, if a driver is stranded and can't get out of a car safely or been forced to stop in a live traffic lane.

The technology can also be used to report a hazard on the road such as a vehicle spotted travelling in the wrong direction.

Yet despite its potential to save people's lives, many drivers, says the organisation, have no idea how to use it.

Mel Clarke, customer services director at National Highways, explains: "Safety is our priority at National Highways.

"The emergency call (eCall) system and its SOS button could save lives and revolutionise road incident response on the roads, yet our research shows that most people do not know about it.

"I urge drivers to check if they have this safety feature installed, particularly if your vehicle was manufactured since April 2018, and to follow our advice about how and when to use it."

All new types of car and van built since April 2018 should have the eCall system fitted as standard. While the system is automatically set-off in an accident, the SOS button inside the car is normally found near the top of the windscreen or on the steering wheel.

National Highways says it is now working with the motoring industry and manufacturers to promote this little-known safety feature.

Mike Hawes, chief executive at Society for Motor Manufacturers and Traders (SMMT) said: "SMMT is pleased to be working with National Highways to build greater awareness and understanding of the emergency call (eCall) system its SOS button functions in vehicles.

"This initiative is vitally important to inform and remind consumers of their cars’ additional safety measures including the ability to call for assistance in times of trouble."

By the end of 2025, more than 12.6 million cars and vans are expected to feature the emergency call (eCall) system.

Steve Gooding, director of RAC Foundation said: "There are so many clever high-tech elements being built into modern motor cars that it’s all-too-easy for motorists to miss the ones – like eCall – that could be the most valuable in the event of a road incident.

"Knowing how to work the infotainment system could take the strain out of a long drive, but knowing how and when to use eCall could save lives.”

To learn more about the eCall SOS system click here.