It is believed the boy hit by an ambulance in Bath is 14-years-old.
He is in a serious condition after suffering a "significant" head injury.
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Tony Davies was the first civilian to reach Pc Palmer after he was stabbed during the Westminster attack.
Defiant Londoners put on a show of solidarity for the victims of the Westminster terror attack at a vigil in their honour.
Weather set to improve with plenty of sunshine by Saturday