National Highways can now shut both M4 carriageways at junction 4B overnight for about six months from 12 October for bridge deck repairs. Diversion via junctions 4 or 5.
National Highways has made an order that lets it close both carriageways of the M4 at junction 4B, under the M25, overnight for about six months from Monday 12 October. The work is bridge deck and carriageway repairs at M25 junction 15, which is the same interchange.
The statutory notice was published on 7 October. The order came into force on 10 October and can run for up to 18 months, ending when the work is finished.
What the order allows
- Which road: both carriageways of the M4 between the exit and entry links at junction 4B. That is the stretch directly under the M25.
- When: overnight only, within these maximum windows:
- Monday to Thursday, 10pm to 5.30am
- Friday, 11pm to 6am
- Saturday, 8pm to 10am
- Sunday, 10.30pm to 5.30am
- How long: approximately six months, starting on or after Monday 12 October 2026.
- Diversion: traffic in either direction is sent along the M4 to junction 4, the Heathrow spur, or junction 5 at Langley, and back.
- Why: bridge deck and carriageway repairs “and all associated works”, in the interests of road safety while contractors are on the structure.
An order is permission, not a timetable. National Highways publishes the actual nights in its seven-day closure report, and that is where each closure will appear, usually a few days ahead.
What is already booked for the first week
The report covering Friday 9 to Thursday 15 October lists no full closure of the M4 at junction 4B. It does list four nights of work at the interchange:
| Night | What closes | Hours |
|---|---|---|
| Monday 12 October | M25 anti-clockwise at junction 15, between the exit and entry slip roads | 10pm to 5.30am |
| Tuesday 13 October | Link from the M25 anti-clockwise onto the M4, both directions | 10pm to 5.30am |
| Thursday 15 October | Link from the M4, both directions, onto the M25 clockwise | 10pm to 5.30am |
| Thursday 15 October | M25 anti-clockwise at junction 15, between the exit and entry slip roads | 10pm to 5.30am |
The two M25 carriageway nights are listed as maintenance. The two link road nights are listed as urgent carriageway and safety fence repairs. The same link roads were shut on 8 and 9 October and on 4 October for similar reasons.
The same job was first notified in May
A notice of intent for the same works, with the same reference series, appeared on 20 May 2026. That version described closures of the M25 carriageways at junction 15, lasting around seven months from 13 June, with preparatory work in June and July and the main works from September to December. The new order names the M4 carriageways instead, and starts the clock again on 12 October, so the main phase appears to have moved.
What it means for you
- The Saturday window is the one to watch. A closure from 8pm on Saturday to 10am on Sunday takes in a Sunday morning, not just the small hours.
- Heading east to the M25 from Slough, the diversion keeps you on the M4 to junction 4 and back. Allow an extra 15 to 20 minutes on a night when the closure is on, and more if the junction 4B link roads are shut at the same time.
- Heading west from Heathrow or the M25, expect to be taken past the junction to junction 5 at Langley and turned round. The A4 through Langley and Colnbrook is 20mph in the borough, so it is not a quick alternative.
- Colnbrook and Poyle residents will see diverted traffic at junction 5 and on the A4 on closure nights. That is the junction the diversion uses.
- Check before a late journey. The seven-day report is updated at about 3.30pm on working days and runs a week ahead. We carry the Slough rows each week on our roadworks and travel page.
The order is published by National Highways under reference NH/SE/2026/M25/51. Queries go to its customer contact centre on 0300 123 5000.
Have your say