Mystery surrounded the 'chemical death' of a man after police closed down parts of Mitcham to protect the public from harm last year.

Today a coroner ruled 36 year-old Jamie Thomson accidentally died after innocently experimenting with cyanide in his garden as part of a new hobby.

Mr Thomson died in the early hours of November 16, 2015, after coming into contact with chemicals at the home he shared with his mother in Carshalton Road, Mitcham.

Westminster Coroner’s Court heard today that Mr Thomson was an extremely intelligent but chronically depressed man who had lost both his father and his grandmother while he was studying physics at Royal Holloway University.

November 18: Tributes paid to Jamie Thomson after chemical exposure death in Carshalton Road, Mitcham

He had begun to take an interest in creating salts and crystals from chemical reactions in his garden shed in the months before he died, and on the evening of November 15 was conducting an experiment using the chemical potassium ferricyanide.

Your Local Guardian:

A dog left indoors in Carshalton Road

Potassium ferricyanide, often used in photography, is not a restricted substance and was legally bought by Mr Thomson over the internet.

It can become extremely toxic if heated or mixed with acid.

The court heard Mr Thomson had not seemed depressed that evening, and after eating dinner with his family had gone into the garden and heated the chemicals in a metal cup on a grill while he performed his experiment.

HM assistant coroner Dr Shirley Radcliffe said it had been “breezy” in the garden that evening.

She said: “Mr Thomson, for whatever reason, felt it would be safe to heat potassium ferricyanide in his garden.

“He wasn’t wearing breathing apparatus and at some point during the heating he inhaled cyanide gas, which we all know is extremely toxic.

November 16: Man dead after "coming into contact with chemicals" at Carshalton Road home in Mitcham

“There’s nothing to suggest Mr Thomson undertook the heating for the purpose of ending his life. This seems to be an utterly tragic accident.”

Mr Thomson went to his bedroom at 10.30pm that evening, and was discovered face down and unconscious in the bathroom by his mother at 2am.

Multiple attempts to resuscitate him failed, and Mr Thomson was pronounced dead at St George’s Hospital, Tooting, at 5.09am on Tuesday, November 16.

Blood samples showed an incredibly high level of cyanide in his blood stream, and although his cause of death was registered as cyanide poisoning, a post mortem was not carried out due to the potential risk to hospital staff.

At the time, police shut down Carshalton Road and searched neighbouring homes using specialist protective equipment until they could establish that there was no further risk.

Your Local Guardian:

Mr Thomson had a history of severe chronic depression and suicide attempts, and was hospitalised in December 2013 after attempting to take his own life using chloroform he had made himself from household items.

However, his social worker Yolanda Nelson, of the Mitcham Recovery and Support Team, said there had been a noticeable improvement in the months leading up to his death, adding: “I wouldn’t ever say he was happy, but seemed more content.”

Dr Radcliffe described Mr Thomson as “a bright young man” who did not make friends easily and suffered a “very chronic form of severe depression for many years.”

She added: “In the months before his death he seemed to be more stable. He made improvements. He found things he could be interested in.

“One of these was making salts and crystals from chemicals.”

After the ruling of accidental death, Mr Thomson’s mother Susan said: “We are very happy with the result of the inquest, and I would like to extend our thanks to everyone who helped Jamie when he was with us.”