The prescription of conventional medication could plummet following today's legalisation of medicinal cannabis, with campaigners now set to ratchet up pressure on the government to legalise recreational cannabis, VICE can reveal.

A large majority (60 percent) of respondents to a study commissioned by the United Patients Alliance – which represents the interests of medical cannabis patients in the UK – said they had substantially reduced the amount of pharmaceutical drugs they were taking to manage a host of conditions after beginning to take cannabis medicinally.

The study also suggested that 76 percent of the British public would be prepared to consume cannabis-based medicines if prescribed by their doctor, with 65 percent of respondents saying they would grow the class B drug themselves if it was decriminalised.

This news comes after a new poll found that the UK overwhelmingly backs the full legalisation of cannabis, indicating a dramatic shift in public opinion since May, when support and opposition for the move was almost even. This change follows the considerable media attention given to Billy Caldwell earlier this year, which propelled the medicinal benefits of cannabis into public consciousness.

The new study, commissioned by Volteface – a think-tank with links to the Cameronite faction of the Tory party – also suggested that more than 6 million people will ask their doctor about accessing cannabis medicines, a substantial rise on the estimated 1 million people who currently use cannabis to treat their conditions.

From today, however, legal access to medical cannabis-based products will only be provided to people who have an "unmet special clinical need that cannot be met by licensed products", with the inadequacies of the interim panel system fuelling speculation that the new system may not satisfy the needs of hundreds of thousands of patients.

Meanwhile, the recent legalisation of recreational cannabis in Canada – a country with strong historical links to the UK, which is not known for reckless policy making – has given politicians in the UK food for thought.

MPs and sources close to the government told VICE they did not envisage any relaxation of the current laws around recreational cannabis under the current government, with the prime minister known to be strongly opposed to any such move.

"Not under Theresa May, but perhaps another," said one Tory MP. "At some point there will be a contest, and it depends on how much evidence from Canada and the US there is when it comes."

It is understood that potential Tory leadership contenders – such as Penny Mordaunt, who has previously expressed support for homeopathic remedies, and Michael Gove, whose former justice and policing advisor, Blair Gibbs, now works for the Centre for Medicinal Cannabis campaign group – remain open-minded privately. "Prohibition is no longer seen as the smart and responsible policy," Gibbs said recently.

An upcoming party review will see some Tory MPs push for legalisation of recreational cannabis to become Conservative, and therefore government, policy. Earlier this summer, an influential right-wing think=tank, The Institute for Economics Affairs, called for full legalisation, describing the potential move as a "win-win", while estimating the current black market is worth £2.6 billion a year.

There is also a belief that the business case for legalisation could become insurmountable. A significant amount of the global investment in cannabis industries comes from the City of London, and a source predicted companies will soon be wining and dining MPs, and paying for them to go to Canada in an attempt to persuade them of the benefits.

It appears that many of the campaign groups behind the push for the legalisation of medicinal cannabis – some of whom are funded by firms with interests in an economic "green rush" – are now turning their sights to legalisation for recreational use, as the discussion around the drug increasingly enters the public sphere.

Campaigners note that law enforcement agencies may struggle to distinguish between an individual using cannabis for medicinal purposes and somebody using cannabis recreationally. "This could end up in a bit of a mess, which could work in favour of arguing for a recreational market," an influential campaigner said. "I've never known an industry better run by criminals than government."

Anxiety around full legalisation has centred on the perceived risk that cannabis poses to young people's mental health. However, leading medical institutions, such as the Royal College of Physicians, have recently announced that they will be reviewing their own policies.

Any change in the college's position could influence government thinking, since its members advise cabinet ministers on the misuse of drugs and mental health issues. The largest ever study on the links between predisposition to schizophrenia and cannabis use found weak evidence for a causal link between the two.

Elsewhere, high-profile politicians, such as former Tory leader William Hague, and public figures like Bernard Hogan-Howe, the UK's most senior policeman until he retired last year, have also expressed their support for reform.

They join a whole host of police chiefs who are advocating for changes, including Arfon Jones, the police and crime commissioner for north Wales, and Mike Barton, who leads Durham police force. "Prohibition does not work," Barton said recently. "We are creating a latter-day mafia in the UK."

A further 33 PCCs have said they do not believe criminalisation is necessary, while the Police Federation is calling for an entirely new approach to drug policy after conceding prohibition has failed.