At about 3.20pm on Monday, a lorry and three cars were involved in a crash on the eastbound carriageway between junctions 5 and 4b.
Four have now left hospital but one woman, the driver of a BMW, remains in hospital in a critical condition.
Anyone who saw the crash or any of the vehicles involved prior to the collision can contact PC Melanie Todd at Three Mile Cross Roads Policing on 101, quoting URN 933 19/05.
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