Police are appealing for a witness to a serious assault to come forward.

The man told people arriving at the scene of the attack on a 23-year-old man in Ship Street, Brighton, that he had seen the attack.

But no one took his name and address because they thought the incident, which happened at 3am on Saturday, was not serious.

When police arrived the man had left the scene.

The victim is in a critical condition with head injuries at Hurstwood Park Neurological Centre, Haywards Heath, and police are desperate to track the witness.

Detective Sergeant Dobs O'Brien, of Brighton CID, said: "We believe the victim was seriously assaulted.

"A man of Hispanic or foreign appearance, who had dark hair and was wearing a blue denim jacket could be the key to finding out what happened.

"He did offer to give details but at the time nobody realised how serious the incident was."

The victim is believed to have been involved in an argument prior to the assault.

Two men aged 18 and 23 from Hove were arrested nearby and have been released on police bail.

Anyone who witnessed the incident, which happened near the junction with North Street, should call Mr O'Brien on 0845 6070999 or Crimestoppers on 0800 555111.