Detectives seized their biggest-ever haul of a designer drug after police pulled over a driver for going through a No Entry sign.

The routine stop led to the discovery of a huge cache of crystal MDMA - a highly pure form of Ecstasy - at a house being used as a cannabis factory.

Detectives seized more than 20kg of compressed cannabis skunk and resin and hundreds of cannabis plants when they raided the house in Cowfold, near Horsham.

The total street value of the drugs seized is thought to be over £200,000, of which the 3.5kg of crystal MDMA was worth £130,000.

It has only been found in small amounts in Sussex before and police believe it may be one of Britain's biggest seizures of the drug.

Crystal MDMA is twice as pure as Ecstasy pills. A single gram costs up to 20 times as much as one pill.

Because of its strength, police and drugs charities believe the new designer form of Ecstasy can catch users off guard and cause seizures.

It is the same as MDMA powder but is sold in bigger grains, or crystals.

Crystal MDMA is grainy or sandy in texture. Users place the crystals under their tongue and allow them to dissolve.

Some experts believe the new crystal format is a marketing gimmick to try to attract drug users for whom Ecstasy pills have become old-fashioned.

The Cowfold drugs factory was found when police stopped a man in Brighton on January 21 for driving through a No Entry sign.

When they searched his car they found eight kg of cannabis in the boot.

The investigation led detectives to a house in Station Road, Cowfold.

They spent three days searching the property last week gathering evidence and seizing substances for analysis.

They found 22 kg of compressed cannabis in different forms and 3.5 kg of crystal MDMA.

One of the bedrooms in the house was home to an advanced indoor-growing system with hydroponic lightbulbs and several hundred cannabis plants.

Detective Inspector Jo Banks, who is leading the Horsham CID investigation, said: "The scale of this seizure has prevented drugs with a street value of over £200,000 from being distributed within Sussex.

"A significant investigation has been launched."

Anyone with information about this investigation is asked to call on 0845 6070999 quoting Operation Kilkenny or Crimestoppers confidentially on 0800 555111.

Maxwell Rousell, 37, of Station Road, Cowfold, appeared by videolink at Brighton Magistrates' Court yesterday charged with having cannabis and ecstasy with intent to supply and being involved in the cultivation of cannabis.

He was remanded in custody to reappear before magistrates again on February 14.

CRYSTAL MDMA - THE FACTS * MDMA, or methylenedioxymethamphetamine, is the chemical which provides the 'hit' in Ecstasy.

* While Ecstasy normally only contains between 50 and 150mg of MDMA per 300mg pill, crystal MDMA or MDMA powder is up to 95 per cent or even 100 per cent pure.

* A gram of crystal MDMA sells for between £40 and £60, while the average price of an Ecstasy pill is about £3.

* The vast majority of Ecstasy in Britain is manufactured in 'super-labs' in the Netherlands and imported.

* Crystal MDMA varies in colour and is different from MDMA powder. White crystals can look the same as 'crystal meth', another relatively new drug, and have the same nickname - 'ice'.

* According to the charity Drugscope, crystal MDMA has caused several drug-induced seizures and overdoses because of its high purity.