One lane is closed and there's queueing traffic due to an accident involving a lorry on the M4 westbound between J16 A3102 / B4005 (Swindon West) and J17 A350 / A429 / B4122 (Chippenham).
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Becky Watts allegedly told a friend that Nathan Matthews, who is on trial for her murder, described how he would kill her in 2013.
Five people have been arrested after clashes between football fans and police before a Swindon - Oxford match on Tuesday night.
Nathan Matthews, the step-brother of Becky Watts, has admitted to killing the teen - but denies he murder her.