Two policemen were stabbed and one was also headbutted as they tried to detain a teenager earlier today.
The officers were taken to hospital for treatment and one needed surgery for his injuries. The assault began when the officers approached two youths acting suspiciously in Acton, west London, in the early hours of the morning.
Police say one of the suspects, aged 17, became aggressive and attacked the officers.
More officers arrived and the teenager was arrested on suspicion of attempted grievous bodily harm and possession of an offensive weapon.
He was taken to a north London police station where he remains in custody.
Both officers received First Aid at the scene after suffering stab wounds to their hands before being taken to a north London hospital.
The officer who was also headbutted has been discharged, but the other officer was stabbed so badly he requires surgery.