Why is the M25 closed this weekend and how bad will traffic be?

Sign up to Simon Calder’s free travel email for expert advice and money-saving discounts

Get Simon Calder’s Travel email

“Stay home weekend”: that is the appropriate slogan between 15 and 18 March for motorists who normally use the southwest quadrant of the M25 motorway.

From 9pm on Friday 15 March to 6am on Monday 18 March 2024, National Highways is to shut the M25 in both directions between junctions 10 and 11. These are key intersections on the southwest quadrant of the motorway. Junction 10 is where the M25 meets the A3 to Guildford and Portsmouth, with many motorists also accessing Chessington World of Adventure. Junction 11 serves the key link of the A320 between Staines and Woking, as well as the A317 to Weybridge.

National Highways says the closure is “to demolish the Clearmount bridleway bridge and install a very large gantry”. It says: “Without a full closure of the M25 at this junction, it would be impossible to safely demolish the overbridges and install the new gantry.”

Normally up to 6,000 vehicles per hour – or 100 cars, coaches and trucks per minute – use the five-mile stretch of the M25 at weekends.

The organisation has prescribed a diversionary route that more than doubles the five-mile distance between the two junctions. National Highways is warning “only travel is necessary”.

Travellers accessing Heathrow and Gatwick airports will be affected, as will many motorists heading for Channel crossings in Kent.

How bad will it be? These are the key questions and answers.

Why is the M25 closed?

National Highways says it is part of a “major project to make journeys safer and reduce pollution”.

The organisation says: “The Junction 10 improvement scheme will see an increase in the number of lanes to make journeys safer and improve traffic flow. It will also make it easier and safer to enter and exit the M25.

“It will also reduce the pollution caused by traffic jams.”

Has this occured before?

Not during the day; there have been occasional night closures when traffic is very light.

The final link in the M25 motorway around London – between London Colney and South Mimms – was opened to traffic by then-prime minister Margaret Thatcher at 9.30am on 29 October 1986.

Since then accidents, congestion and roadworks have caused countless problems. Yet never has a crucial stretch of one of Europe’s busiest motorways been completely closed for a weekend.

This will be the first of five closures between now and September 2024.

What’s the advice for drivers?

Jonathan Wade, National Highways Project Lead, says: “Drivers should only use the M25 if their journey is absolutely necessary.

“We have spent months planning for these closures and making sure there are diversion routes in place, but there will still be heavy congestion and delays.”

The diversion route involves the A3, the A245 and the A320.

“Taking the M25 in the other direction to avoid our closure is also an option,” National Highways says.

The organisation’s senior project manager, Daniel Kittredge, urges motorists not to follow recommendations of their satnav, and instead stick to the official diversion. The fear is that gridlock could quickly spread across northwest Surrey.

“If people move away from diversion routes that we prescribe, it creates additional issues in different parts of the road network,” he says. “The majority of the time that will be local roads, so that really impacts residents in those particular areas.”

Alice Simpson of RAC Breakdown says: “The most obvious diversion routes are likely to get extremely congested.

“It’s always best to set off as early as possible and avoid travelling during peak hours like late morning and lunchtime.

“As the M25 is notoriously one of the busiest routes in the country any increase in drivers could lead to more breakdowns, and even more jams.”

She says motorists heading for Heathrow or Gatwick airport “will have to leave a lot more time to get there”.

Before the M25 opened, journeys between the UK’s two busiest airports were extremely slow and complex by road. Coach links between Gatwick and Heathrow are also likely to be disrupted.

Will any coaches be running?

Yes. A spokesperson for National Express said: “National Express will continue to operate services along diverted routes during next weekend’s closure of the M25 between junctions 10 and 11.

“Delays are expected and customers are advised to allow plenty of time for their journey.

“We are contacting customers who are affected by the weekend’s diversion to offer a free amendment to their ticket should they wish to change their travel plans.”

A spokesperson for FlixBus said: “Almost all our network will be unaffected by M25 closures, delivering reliable, affordable transport as usual, with only a handful of services between Bristol and South Wales terminating at Heathrow between 15 and 18 March instead of going through to Gatwick airport.

“Passengers who were booked onto these Gatwick services have been given the option to either change their date of travel or receive a full refund.”

Any alternative route between Heathrow and Gatwick airports?

Yes. The easy option is to take the Elizabeth Line from Heathrow to Farringdon in central London, which has a direct connection to Thameslink trains. The journey time is about 90 minutes.

Maddeningly, National Rail does not offer fares for the whole journey. The solution is to buy one ticket from Heathrow to East Croydon and another from there to Gatwick. The total single fare is £22.30.

With there be other problems that weekend?

Yes. Traffic on the rest of the M25 is likely to be much heavier; for example motorists from Birmingham or Oxford taking the M40 to London may decide to head for Gatwick via the northern and eastern sections of the M25, increasing congestion.

Many key rail links across Great Britain are closed – with the absence of trains from London Marylebone to Aylesbury possibly exacerbating problems caused by the M25 closure.

Additional rail closures: