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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Some morning brightness on Boxing Day but cloud increasing, with rain, sleet and snow, spreading in late afternoon. Turning windy.
Starting cold and dry Boxing Day. Wet and windy later.
The Met Office has issued a yellow weather warning for the risk of rain turning to snow later on Boxing Day in parts of the Anglia region