Police investigating the death of a man in Norwich have confirmed there is no link to recent incidents in Suffolk involving the 'Superman' ecstasy pills.

A man in his 20s died and another remains critically ill in hospital after being taken unwell at a property in Norfolk Street, Norwich, yesterday morning.

Tests on substances seized have revealed traces of a drug known as AMT – a former legal high which from yesterday was made a Class A drug.

Police are warning about the dangers of using the substance – which is not only illegal but can be highly dangerous to health and possibly fatal, as seen in this case.

Detective Chief Inspector Andy Ninham said: 'Tests on substances have confirmed our initial suspicions that this incident was related to the use of illegal substances. Officers searched the property in Norfolk Street yesterday and seized a number of items including cannabis and white powder, thought to be Class A drugs.

'The investigation continues and I would reiterate my comments made yesterday about banned substances in that they are illegal and highly dangerous to your health.'

Norfolk police's drug liaison officer, Detective Constable Steve Hamilton, said AMT (alpha-methyltryptamine) was a hallucinogenic stimulant drug which could be very active in small doses, therefore increasing the chances of overdose.

He said: 'AMT is available as white and coloured powders, capsules, tablets and in liquid form. It is often sold as a new psychoactive substance (legal high) however due to the potential harm associated with its use; AMT was made a Class A Controlled Drug under The Misuse of Drugs Act 1971 yesterday.

'I would urge people not to be tempted in taking AMT, or any other illegal drug, for the simple reason you do not know what it contains or the effect it will have on you.'

Four people, three men aged 22, 30 and 33, and a 20-year-old woman, were arrested on suspicion of supplying a controlled drug and questioned by detectives yesterday. All suspects have since been released on bail until February 5 while enquiries continue.