Police kept watch on a chemist suspected of making drugs for months before he was arrested, a jury heard.

Detectives monitored the daily movements of Casey Hardison, who is accused of manufacturing class A drugs with a street value of up to £5 million at a home-based factory in Ovingdean, Brighton.

The makeshift lab allegedly found in one of the bedrooms at the detached house Hardison rented in The Vale, is believed to be the most sophisticated and complex discovered by police in the UK for 25 years.

At his Lewes Crown Court trial Hardison, 33, a committed advocate of drug legalisation, has denied five charges of producing class A drugs, including LSD and mescaline. He has denied possessing 145,000 doses of LSD with intent to supply, possessing 5-Meo-DMT and smuggling ecstasy from the UK to the United States.

The court heard police set up Operation Pathfinder to organise covert surveillance of Hardison in the autumn of 2003.

Secret cameras recorded the American's movements. One was set up in a field opposite his three-bedroom, £1,100-a-month home.

In February 2004, when police suspected he was planning to move, officers decided to arrest him.

At the Sanctuary cafe in Hove Hardison was arrested on suspicion of manufacturing illicit mind-altering drugs.

Detective Sergeant Tony Pike said officers were concerned there was a risk of contamination from the potentially dangerous chemicals Hardison had allegedly been using and he was given a protective hooded overall to wear before being taken to the police station.

The following day a team of specialists wearing "spaceman" type chemical protective suits and helmets moved in to start searching his house at Ovingdean.

The team included experts from the National Crime Squad's illicit laboratories team, the National Crime Intelligence Unit, scenes of crime officers, scientists from the Forensic Science Service and fire officers.

Det Sgt Pike said the lab turned out to be so complex that after searching the premises all day the team decided to ask for extra help and more specialists were drafted in.

The officer, who is regarded as a specialist drug investigator, told the jury it was rare to find makeshift labs.

He said: "In all likelihood this is the most complex laboratory found by police for over 25 years.

"The general consensus is it is the biggest find in the country since Operation Julie in the late Seventies in Wales, which was producing huge volumes of LSD. This laboratory is more sophisticated and complicated."

The trial continues.