A 19-year-old man is seriously ill in hospital after apparently taking a new and relatively unknown drug.

The man, from Brighton, is among four people affected after a rave at Biggleswade, Bedfordshire, in the early hours of Sunday.

He is in a critical but stable condition in intensive care at Stevenage after he started suffering fits.

An ambulance was also called for a second man, who was well enough to speak to detectives yesterday afternoon.

Two more people at the rave went to Milton Keynes General Hospital on Sunday evening, complaining of similar problems.

One is in intensive care unit, the other is in a stable condition.

Officers who spoke to other party-goers were told the two men may have taken a drug called DO1, DOI or DO9 which has recently appeared on the illegal drugs scene and about which little is known.

DOI is a type of amphetamine but its effects are hallucinogenic rather than stimulating. It was developed by the Californian chemist Alexander Shulgin, who promoted the use of ecstacy.

Detectives warned anyone who may have taken it to seek medical help immediately.

Bedfordshire Police said the drugs could have been bought at the rave in factory premises in Biggleswade or at a separate event near Milton Keynes which was broken up by Thames Valley officers hours earlier.

About 250 people were at the rave and most of those travelled from Buckinghamshire when the Milton Keynes event was closed.

A police spokesman said: "It is unclear at present whether any of the people in hospital actually took this drug or what form it came in - whether tablets or strips - but officers are warning anyone who was at the rave in Biggleswade they should under no circumstances consume any drug they have in their possession from the weekend."