A partial closure of the M25 and industrial action by train drivers will lead to travel chaos throughout the weekend, experts have warned.

Britain’s busiest motorway will be shut in both directions between junctions 9 and 10 in Surrey from 9pm on Friday until 6am on Monday while concrete beams for a new bridge are installed.

For each day of disruption, 270,000 journeys are expected to be affected, according to the AA, as drivers take to the roads to make the most of the warmer weather.

Saturday could be the hottest day of the year, with temperatures of 27°C expected in some areas of south-east England.

The delays are likely to be exacerbated by more disruption on the trains.

People hoping to travel by rail have been warned of reduced services throughout the UK because of a ban on overtime as part of industrial action by train drivers belonging to Aslef.

National Rail said the ban, which began on Monday and runs until Saturday, will lead to some disruption to timetables. Major rail companies are warning that trains that are running will be busier than usual and those planning to travel are being advised to allow extra time for their journeys.

It follows a three-day strike by drivers which caused the cancellation of train services from Penzance to Aberdeen.

The Aslef strikes form part of a pay disputed that has continued for nearly two years. There was hope this week of negotiations restarting between Aslef and train operators with the Rail Delivery Group (RDG), which represents rail companies.

No meetings have been held between the two sides for a year, while Government ministers have not met representatives from Aslef since the start of 2023.

Martyn James, a consumer rights expert, recommended planning “for the worst” as many people are likely to want to travel to make the most of the sunshine.

He told i: “Have a think about whether it’s worth getting on a train. Roads will also be busy and you don’t want to lose half your weekend in a traffic jam.

“Undoubtedly there are going to be some big delays and that could spoil everything.”

Mr James said people should make back-up plans that could include travelling by coach or alternate driving routes that don’t involve the M25.

He said people with tickets to special events should check the refund policy if they are unable to get to it and be wary of surge pricing that is sometimes used at popular destinations.

National Highways said diversion routes are planned to cope with the partial closure of the M25, which will take cars on a 19-mile journey on A roads, crossing from Surrey into London.

The routes will enter the capital’s Ulez area. The highways authority said “no enforcement action will be taken” but said anyone who ignores official diversion signs in an attempt to find shorter alternative routes will be liable for the £12.50 daily Ulez fee if their vehicle does not meet minimum emissions standards.

Failure to pay the charge when required can lead to a £180 fine, which is reduced to £90 if paid within 14 days.

The RAC told drivers to avoid travelling if possible and pack extra food and drink if they do, as the closures are likely to bring long delays for thousands of drivers.

Alice Simpson, breakdown spokesperson at the RAC motoring group, said: “The closures also coincide with the retrofitting of new emergency areas on all-lane-running stretches of the M25, meaning delays are likely between junctions 5 and 7 in Surrey and Kent and junctions 23-27 in Hertfordshire and Essex.

“With weekend temperatures reaching 25°C or even higher, it’s likely that routes around the 23-mile diversion will be busy as people make the most of the fine weather and jump in the car for day trips.”

She said holidaymakers heading to Gatwick or Heathrow should leave an hour earlier than usual anyone anyone heading to Chessington World of Adventures, a theme park near the diversion route, should expect delays.

The M25 closure is the second of five planned weekend closures which are part of a £317m project to improve Junction 10.