A GYM-GOER from High Wycombe died after drinking a lethal chemical he thought would help him lose weight, a court heard.

Sean Cleathero drank a sachet of the Dinitrophenol (DNP) drug mixed with water at a Wycombe gym on October 16, 2012, and died hours later in hospital.

Jason King, 41, Peter Purkins, 47, and Jamie Chivers, 44, are on trial at the Old Bailey accused of his manslaughter – they all deny the charges.

The court heard Purkins and Chivers were co-owners of Apollo Fitness, the company that ran the gym, and Precision Laboratories, the substance supplying firm.

Mr Cleathero, am Apollo gym member of seven months, ordered the powder from Purkins after previously using DNP tablets that had not worked.

The court heard Chivers dropped off the sachet at the gym and King, an employee, handed it over the counter to the 28-year-old and advised him to dissolve it in water before drinking it, the prosecution said.

The jury was shown CCTV footage of the father-of-one consuming the bright yellow liquid.

Further footage shows Mr Cleathero sweating profusely upon leaving the gym after a work out.

Prosecutor John Price QC said: “The minute he drank the contents of that glass, he was a dead man, because there's no antidote.

“By the time he leaves, the DNP which you saw him take was beginning to have the toxic and ultimately lethal effects on him.

“He couldn't stop sweating, even long after he finished his workout and he was starting to struggle to breathe.”

An ambulance was called to an address Mr Cleathero shared with his grandparents and he was rushed to Wycombe Hospital, where he died eight hours after drinking the substance.

The court heard Mr Cleathero’s body temperature soared to 42C as he suffered a heart attack and kidney failure.

A post mortem ruled the DNP drug was the cause of his death.

Mr Price told jurors DNP was not a controlled drug and had a legitimate use as an insecticide or herbicide, but it was not fit for human consumption.

Nine years before Mr Cleathero died, the Food Standards Agency had advised that DNP was "extremely dangerous to human health" following the death of a man in Finland.

Mr Price said Apollo Fitness and Precision Laboratories was a 'veneer' for an illegal steroid dealing ring and the defendants would have known about DNP’s effects.

He added: “[The defendants] knew the truth of DNP within the industry in which they operated, it will have been notorious.

“If they did not know as they may say, well the answer to that is if they were involved in the commercial supply, selling it, to the public for consumption, then they ought to have known.”

The court was told Chivers had admitted to perverting the course of justice after he "forgot to delete" CCTV footage showing him deleting incriminating video from the gym earlier in the week.

Chivers, of Spring Gardens Road, Wycombe; Purkins, from Heather Walk, Hazlemere; and King, of Hazell Road, Prestwood, along with Laura Hague, 23, of Orchard Grove, Chalfont St Peter, deny charges of producing and supplying anabolic steroids.

Hague, who the prosecution claims was caught in a serious of text messages with Chivers attempting to remove incriminating evidence, also denies perverting the course of justice.

The trial continues.