Traffic is queueing on the westbound carriageway of the M4 near the junction for Slough West after a multi-car pile-up.
Two lanes were closed following the accident near the exit slip road for junction 8/9 for Maidenhead but have now been re-opened.
Updates to follow.
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The Met Office has issued a yellow alert for Windsor and Maidenhead, Slough and Wokingham, warning that rain moving eastwards across the south of the country may turn to snow in some places.