Spanish midfielder Juan Mata is expected to complete his record move to Manchester United today.
United have reportedly had a bid of £37 million accepted by Chelsea, and Mata is expected to undergo a medical before signing a four-and-a-half year deal.
Mata, 25, has failed to command a regular starting berth under Jose Mourinho and is looking to move on ahead of this year's World Cup.
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Paramedics were on standby outside the police cordon as armed officers stood by the property.
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The action comes on top of an emergency timetable which has seen hundreds of trains a day being axed.