M25 near Heathrow to close anticlockwise at junction 15 on two October weekends

The anticlockwise M25 will close at junction 15, where it meets the M4 next to Heathrow Airport, overnight on two weekends this month.

National Highways said the anticlockwise carriageway will be closed between the M4 slip roads from 8pm on Saturday 17 October to 10am on Sunday 18 October, and again from 8pm on Saturday 24 October to 10am on Sunday 25 October.

The clockwise carriageway and all the links between the M25 and the M4 will stay open throughout the works.

Why the road is closing

The closures are for preparatory work on bridge repairs at junction 15, also known as the Thorney Interchange, which is junction 4b on the M4. National Highways is getting ready to replace the bridge expansion joints on the junction, a project expected to run into 2027.

Expansion joints are the gaps built into bridges that let the structure expand and contract with changes in temperature. They wear out over time and have to be replaced to keep the road safe.

National Highways has said that a series of extended overnight closures will be needed in 2027 to do the replacement itself. The joint on the anticlockwise carriageway will be replaced first. The clockwise joint is due to follow later in 2027, and those dates have not yet been confirmed.

Diversion and expected delays

During each closure, anticlockwise M25 traffic will have to leave the motorway at junction 15 and follow a fully signed diversion before rejoining the anticlockwise M25 beyond the closure. The diversion takes drivers west along the M4 to junction 5, then back east to rejoin the M25 at junction 4b.

National Highways expects the worst delays on the Sunday mornings, between 8am and midday. Anyone with an early flight or dropping off passengers at the airport is advised to set off earlier than usual.

Heathrow Airport has also told passengers who plan to use this stretch of the M25 to allow extra time when travelling to the airport during the closures.

The clocks go back by one hour at 2am on Sunday 25 October, which falls during the second overnight closure. Travellers should check their journey times with that in mind.

A busy route for West London

Junction 15 is one of the busiest interchanges on the M25. It links the orbital motorway to the M4 for central and West London, Slough and Reading, and carries a large share of the traffic going to Heathrow's terminals.

Drivers can check the latest roadworks and closures on the National Highways website before they travel. The works can also be avoided by using public transport to Heathrow, including the Elizabeth line, the Piccadilly line and the Heathrow Express.