National Highways will close the M25 anticlockwise carriageway at junction 15, the interchange with the M4 that feeds Heathrow Terminals 2 and 3, from 8pm on Saturday 24 October until 10am on Sunday 25 October. It is the second of two overnight weekend closures this month, following one on 17-18 October, carried out ahead of a bridge expansion joint replacement project due to run into 2027.
The closure sits between the M4 slip roads. The M25 clockwise carriageway and all links between the M25 and M4 stay open throughout, but traffic travelling anticlockwise must exit at junction 15 and follow a signed diversion: west on the M4 to junction 5, then back east to rejoin the M25 anticlockwise via junction 4b.
National Highways says the interchange will be busiest between 8am and midday on the Sunday, and has warned that residual delays are likely to continue on the M25 after the closure lifts at 10am. The agency is advising anyone who must travel during the closure window to plan ahead, allow extra time, and consider alternatives including the Elizabeth Line or Heathrow Express.
The practical risk for passengers is in how the timing is read. A closure billed as 'overnight' can still disrupt a late-morning or early-afternoon departure, because journey planning works backwards from check-in and security to the drive itself. A passenger with a midday flight who needs two to three hours for check-in and security, plus the drive to the terminal, may need to set off while the closure and its aftermath are still affecting traffic, particularly during the stated 8am-to-midday peak.
National Highways confirmed the closure dates and diversion route on its official project page for the M25 junction 15 bridge repairs. The closure and its likely effect on Heathrow-bound traffic were also reported this week by UK regional outlets covering the works.
No flight cancellations or airport-side disruption have been linked to the roadworks; this is a road closure near the airport, not an airport operational issue. Heathrow itself remains open and operating as normal.
What this means for your journey: if you are driving to Heathrow over the weekend of 24-25 October, especially for a Sunday morning or lunchtime flight, build in significant extra time or avoid the M25 anticlockwise near junction 15 altogether. See our /taxis/ and /public-transport/ pages for alternative ways to reach the terminals, including rail options that bypass the closure entirely.