Two lanes are closed and there are long delays due to a fuel spillage and an accident involving two lorries and a car on the M4 westbound between J17 A350 / A429 / B4122 (Chippenham) and J18 A46 (Bath/Tormarton).
Lanes one and two (of three) were closed around 2:45am after a lorry collided with the nearside barrier.
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The Duchess of Cambridge has been on maternity leave since the week before Easter.
The Duchess of Cambridge has been driven to St Mary's Hospital in London in the "early stages of labour", Kensington Palace has said.
Dry, breezy and cool