A second arrest has been made over the death of PC Andrew Duncan after he died from his injuries following a hit and run collision on Friday.
The Met have confirmed a woman has been arrested on suspicion of perverting the course of justice. She remains in custody at a South London police station.
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It was Tom's second marathon in two weeks run in memory of his father, Martin Campbell.
Surrey Police are appealing for witnesses after the driver was seriously injured in the crash in the early hours of Saturday.
The Duchess of Cambridge has been driven to St Mary's Hospital in London in the "early stages of labour", Kensington Palace has said.