The Prime Minister has said video footage that has emerged of MP Mike Amesbury appearing to punch a man to the ground is "shocking".
Mr Amesbury has been suspended from the party and had the Labour whip withdrawn after CCTV footage appeared on Sunday.
Sir Keir Starmer said the party had “moved very swiftly” to respond after the footage was published.
He added: "There is now a police investigation and in the circumstances you'll appreciate there's not much more I can say about that."
Cheshire Police said a 55-year-old man had been voluntarily interviewed under caution in relation to the incident and had since been released pending further enquiries.
In footage obtained by the Daily Mail, the Runcorn and Helsby MP is apparently seen continuing to hit the man as he lies in the street.
Amesbury has been contacted for comment.
A different video, posted on X, purported to show Amesbury shouting and swearing at the man lying in the street in Frodsham, Cheshire.