A former UK government advisor on drugs policy has backed plans for a pro-cannabis rally in Glasgow next month.

Professor David Nutt, an expert on how drugs affect the mind, said the event to be held at Glasgow Green on July 10 is a “peaceful protest against irrational laws”.

Possession of the Class B drug can lead to a five-year jail sentence and similar pro-Cannabis demos in Glasgow have led to several arrests.

Police, the council and the Scottish Conservative shadow justice minister have spoken out against the event which around 450 people are expected to attend.

But Professor Nutt – who was dismissed as chair of the Advisory Council on the Misuse of Drugs in 2009 after saying that ecstasy, cannabis and LSD were less dangerous than alcohol and tobacco – has offered his support.

Read more: Call for cops to take action at Glasgow Green 'Dope Day' rally

The head of the Department of Neuropsychopharmacology and Molecular Imaging at Imperial College London has long advocated the use of some illegal substances to treat patients suffering from everything from anxiety attacks to terminal cancer.

Professor Nutt said: “Stopping this would be a waste of police time and taxpayers’ money. Let's be sensible and allow a peaceful protest against irrational laws.”

On Monday, Shadow justice minister Douglas Ross said cannabis use is “simply not safe” and urged the authorities to “clamp down” on the rally.

Christine Duncan, CEO of charity Scottish Families Affected by Alcohol and Drugs, has backed the MSP.

She said: “Cannabis use, as with other substance use, can and does negatively impact individuals, their families and communities. Like all illegal drugs, you don’t know what you’re taking or how strong it is.”

Yesterday organisers Glasgow Cannabis Social Club insisted the event will “operate safely and peacefully”.

Chris MacKenzie, of the group, said: “If the police feel the need to confiscate cannabis from people, give them fines, a criminal record, restrict someone's right to travel, impact career opportunities, over a plant that is non-toxic, therapeutic and that has been used for thousands of years without death, all in the name of protecting people from themselves, then that's up to them.

“Yes, some people shouldn't consume it and others maybe want help to reduce their consumption or get help with using the herb properly in the right dose and ratio…but cannabis is a billion dollar industry waiting to replace many of our old ways of life and path the way for a sustainable future. “The government can't argue that if we spent those millions generated and invested it in housing and social care and jobs and, of course, psychiatric health, if this even becomes a problem.

“The police should be keeping the peace and making sure there are no crimes being committed that involve a victim. Our events always operate safely and peacefully.

“There really is no concern that I see with people gathering publicly to listen to music, have a picnic, maybe even a BBQ and do something they do every day – well, most of them.”

A spokeswoman for Police Scotland said: “Any criminality will be dealt with appropriately.”

A council spokeswoman said the group had not applied for permission to hold the event at Glasgow Green and “any application to hold an event encouraging the use of cannabis would be refused.”