The Metropolitan Police has issued a new picture of PC Andrew Duncan, who died following a suspected hit-and-run collision in Sutton.
A further two men have been arrested in connection with the crash, after another was remanded in custody accused of causing death by dangerous driving.
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The London Mayor insisted he was "not saying that nationalists are somehow racist or bigoted" after outraging SNP supporters.
The teenagers, aged 19 to 15, appeared in custody at Westminster Magistrates' Court on Saturday, supported by their families.
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