AP
The RAC has warned motorists to avoid travelling on the M25 if possible as construction is underway at junction 9 and 10

Motorists have been warned of lengthy delays this weekend as parts of the UK’s busiest motorway will close for construction.

Junctions 9 and 10 of the M25 will be closed in both directions from 21:00 on Friday until 06:00 on Monday while concrete beams for a new bridge are installed.

Saturday is set to be the warmest day of the year so far, peaking at 26C in south-east England, including around London.

Diversion routes will take cars on a 19-mile detour that will enter London’s ULEZ zone, although National Highways has assured drivers “no enforcement action will be taken”.

However, they have warned that anyone who ignores official diversion signs will be charged the £12.50 daily ULEZ fee if their vehicle does not meet minimum emissions standards.

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

Motorists have been advised to avoid travelling if possible and to pack extra food and drink if they do.

These closures follow a week of major national rail strikes.

Alice Simpson, a spokesperson for breakdown company RAC, said: “Holidaymakers heading to Gatwick or Heathrow should leave an hour earlier than usual and allow plenty of time for parking and security checks.”

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