A businessman who duped his family into helping him run one of Britain's largest illegal drug factories has been jailed for 12 years.

Father-of-five Kevin Hoare, 46, of Bugsell Mill Oast, Hurst Green, near Robertsbridge, had amphetamine sulphate worth £20 million in his barn when it was raided by police.

Officers discovered chemicals which could have been used to produce 660 kilos of the drug known as speed.

After a six-week trial at Lewes Crown Court, Hoare was found guilty of conspiring to produce the drug.

The jury heard how he was helped by his sons Adam, 19, and Russell, 20, of Princes Plain, Bromley; his girlfriend Tracey Thacker, 35, of Vicarage Way, Hurst Green, and handyman Alan Smith, but did not tell them it was illegal.

The four admitted taking part in the chemical-making process but insisted they thought the drug was to treat cancer.

Russell Hoare was found not guilty on Tuesday of conspiring to produce the drug and there were gasps of relief from the public gallery as the other three defendants were cleared of the same charge yesterday.

Kevin Hoare was also found guilty of conspiring to supply the drug along with Graham Pierce, 41, of Greyswood Street, Streatham, London.

Both were given ten-year sentences, with Kevin Hoare's to run concurrently.

Sentencing both men, Judge Guy Anthony said: "This is one of the most serious types of offences involving amphetamine that can be imagined.

"You, Kevin Hoare, got the assistance of your family and girlfriend and did so under the guise of something far more noble than producing a controlled drug.

"Anyone involving themselves in the production of controlled substances must expect severe punishment."

The arrests came after the National Crime Squad put the isolated barn at Bugsell Mill Oast under surveillance last year.

When officers swooped on July 18, they discovered a makeshift laboratory with bubbling vats of chemicals being turned into the drug.

Earlier in the trial, Christine Laing, prosecuting, told the jury: "This is one of the largest illegal drug operations to have been uncovered in this country."

Kevin Hoare used the cover of his legitimate glass-making business to purchase large quantities of chemical components.

The court heard he would take the drugs in a van to Pierce's home in south London. Both men were arrested during a delivery of more than a kilo of amphetamine, worth up to £200,000.

Throughout the trial, Hoare claimed he rented out the barn for £500 a month to a business associate, who he refused to identify in court and referred to only as Mr A.

This mystery man said he was working on a medical research project, which would help to cure cancer.

Defence barrister Michael Oliver told the court: "This was not a massive operation of international proportion.

"The factory may not have been for personal gain but in order to preserve his failing company."