Fifty-nine per cent of people surveyed strongly support or tend to support legalisation of the drug, compared to just 31 per cent who oppose the idea.
Its results show that support for cannabis legalisation is highest amongst younger people. More than two-thirds (68%) of 18-24 year olds support the policy, although almost half (49%) of over 65s believe the same.
Two-thirds (65%) of the public believe cannabis laws should be reformed, though the number is split between the 40 per cent who support legalisation and 25 per cent who prefer decriminalisation.
Under decriminalisation, sale and possession of cannabis would be illegal but it would be regarded as a minor offence as opposed to a criminal one.
The new research marks a dramatic shift in public opinion.
“In only six months, opinion has swung significantly in favour of cannabis legalisation, which Volteface believes is a reaction to the recent developments around medical cannabis,” Liz McCulloch, the think tank’s director of policy, told The Independent.
She said increasing awareness of the harms of the illicit market and Canada becoming the first G7 country to legalise cannabis had also contributed to the shift.
“Cannabis is now firmly part of mainstream political debate and awareness of alternative approaches around the world have made legalisation a viable policy option,” she added.
Two high profile cases involving children and medicinal cannabis caused outrage across the UK over the summer and helped to drive a change in the law.
The government found itself under pressure after a batch of cannabis oil medication was confiscated from Charlotte Caldwell, mother of Billy Caldwell, at Heathrow Airport in June.
The medication helped Billy, who has a rare form of epilepsy, control his seizures.
After a public outcry the Home Office granted Billy a short-term licence to allow him access to cannabis oil.
Alfie Dingley, a seven-year-old boy who similarly used the oil to control epileptic seizures, also made headlines in March when his family petitioned the government for him to be allowed to use medical cannabis prescribed in the Netherlands at his home in Kenilworth.
Following the outrage, Sajid Javid, the home secretary, announced that doctors in the UK will legally be able to prescribe medical cannabis from November.
“The increase in support for legalisation is too significant to see public opinion return to previous levels,” said Ms McCulloch.
“As seen from the Billy Caldwell case, there is an appetite for reform in British politics and momentum is only going to build further.
“Those aged over 65, for instance, have historically been opposed to cannabis reform, so it is significant that 49 per cent of people in this age group now support legalisation.”
The Populus poll also found 76 per cent of people would be willing to consume cannabis as medicine if it was prescribed by their doctor and that the rate was “fairly consistent” across demographic groups.
The survey suggests around 6.7 million people are planning to ask their doctor about accessing medical cannabis.
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