Police are advising drivers to avoid the M25 until mid-afternoon after a lorry fire closed the carriageway on both directions in Hertfordshire.
The section between junctions 21a and 23 near the South Mimms services is expected to be closed until 3pm.
Long tailbacks have built up on surrounding roads.
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Flights have been cancelled, diverted and delayed after a lightning strike overnight knocked out Stansted's aircraft fuelling system.
Sunny spells. Very warm inland. Isolated thunderstorms. Cooler near coasts.
Mostly dry overnight. Some warm sunshine Sunday, however thunderstorms possible.