Drivers are set to face significant delays as a section of the M25 shuts in both directions next month for the second time.

There was a two mile-long traffic jam when the motorway’s first-ever planned daytime closure began on 15 March between junctions 10 and 11 in Surrey – though many drivers followed advice to steer clear of the area until it reopened late on 17 March, meaning long hold-ups were widely avoided.

This time it’s junctions 9 and 10 that will be shut both ways and the stretch of road is two miles longer than last time.

Those set to be those travelling to, from and between the UK’s two busiest airports, Heathrow and Gatwick, are expected to be affected as National Highways has warned it expects long delays.

But is traffic expected to be worse than it was the first time, what are the diversion routes this time and will there be more closures after this one?

Here’s everything we know so far.

When is the closure and how long will it last?

It’s from 9pm on Friday 10 May until 6am on Monday 13 May and will see a seven-mile stretch between junctions 9 and 10 closed – two miles more than in March.

What are the diversion routes?

Though there were fears of severe congestion on diversion routes along A-roads ahead of the first closure, many drivers followed advice to avoid the area, meaning long hold-ups were avoided.

But National Highways senior project manager Jonathan Wade has warned the next shutdown will be “far from a repeat of the previous closure” as the diversion routes are “longer and will be different for over-height vehicles and all other traffic”.

Here are the 19-mile diversion routes, which use the A3 and the A243:

Diversion route clockwise for all but over-height vehicles:
Leave M25 at junction 8, A217 (Reigate). Follow the A217 London, Sutton, (A240) Kingston. After 3½ miles turn left onto the A240 Epsom, Kingston. After 3 miles at the Esso roundabout, turn right onto the A24 (A240) Kingston. Continue for 3 miles and turn left onto the A3 Portsmouth, Guildford. Continue for 9½ miles to the M25 and re-join the motorway at junction 10.

Diversion route anticlockwise for all but over-height vehicles:
Leave M25 at junction 10 to join the A3 towards London. After 9½ miles at the Hook interchange leave the A3 turning right onto the A240 Epsom, Reigate. Continue for 3 miles to the Esso roundabout and turn left onto the A240 Reigate. Continue for 3 miles then turn right onto the A217 Reigate, M25. After 3½ miles turn left to re-join the M25 motorway at junction 8.

Here’s a map showing the closed road and diversion route:

Satnav warnings

Drivers are again being urged to ignore satnavs and only follow official diversion routes to prevent causing gridlock.

Mr Wade said: “Drivers listened to our advice last time which reduced motorway traffic levels by over two-thirds and meant delays were limited.

“Our advice again is please only travel if absolutely necessary and make sure you give yourself extra time if you do choose to use the M25.”

Ahead of the last closure, he warned: “There’s probably a greater risk of congestion by people just doing their own thing and thinking they can perhaps beat the signs and find a shorter or quicker route.

“That will cause further congestion on some of the key junctions so please avoid doing that if at all possible.”

National Highways senior project manager Daniel Kittredge said: “If people move away from diversion routes that we prescribe, it creates additional issues in different parts of the road network.

“Stick on the prescribed diversion route. It’s going to be more suitable for your journey.”

How bad could it be?

It’s only the second scheduled daytime all-lanes shutdown on the M25 since it opened in 1986, so the full extent of possible delays is not entirely clear.

The stretch between J9 and J11 is normally used by 4,000 to 6,000 vehicles in each direction every hour from 10am until 9pm at weekends.

And because the stretch of closed road is longer this time, the diversion route is also 7.5 miles longer than the one last month.

It’s not only drivers who feel the effects; business owners along the diversion route during the last closure said they were forced to make cuts to their services in anticipation of traffic.

Airport warnings

People due to travel to Gatwick and Heathrow could be affected by the closure. Sky News has contacted both airports for comment on the latest disruption.

Last time, Heathrow Airport advised passengers planning to use the affected route to allow for extra time before their flight.

“Passengers using public transport should also be aware that The Airline (between Heathrow and Gatwick) and RailAir (RA2), will be running amended timetables over this weekend, please check with your operator for the latest information,” their statement said.

In March, a London Gatwick Airport spokesperson said: “Passengers driving to the airport are advised to check diversion routes before they travel and allow extra time for potential delays.

“Gatwick’s train station is well-connected and is a great alternative option for people travelling to the airport this weekend.”

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Why is it happening?

Government-owned company National Highways said the action is necessary to enable a bridge to be demolished and a new gantry to be installed as part of a £317m improvement project.

National Highways says the project will increase the number of lanes and make it easier to enter and exit the M25 at junction 10, which is one of the UK’s busiest and most dangerous motorway junctions.

“These improvements will bring long-term benefits to drivers who pass through this stretch of the M25, not to mention pedestrians, cyclists and horse riders who will also see positive changes in the area,” Mr Wade said.

Is this the last closure?

No – it’s the second of five planned full closures between the junctions. The other dates have not yet been confirmed.

National Highways has said it intends to close the M25 for three more weekends this year.

“There will be no weekend closures in June,” it said in a statement.

“The remaining closures will take place between July and the end of 2024. We will be in a position to announce the date of the next closure as soon as the May closure is over.”

The project began in summer 2022 and is expected to last three years in total.