All illicit substances, including heroin and cocaine, should be legalised, according to a former drugs minister who will today become the most senior politician to push for a dramatic change in the strategy for tackling Britain's drug problems.

Bob Ainsworth will argue that it is better for addicts to receive their fixes on prescription rather than relying for their supply on the international criminal gangs that make billions of pounds from the trade.

As a Home Office minister, Mr Ainsworth was responsible for drugs policy and, as the Defence Secretary, he witnessed first-hand the huge opium fields in Afghanistan that supply the West.

Download the new Independent Premium app Sharing the full story, not just the headlines

He will call in the Commons for a fundamental rethink of how the country responds to drug addiction. He will receive the backing of senior MPs of all parties who will argue that the current tough stance on drugs is counter-productive.

Mr Ainsworth told The Independent last night: "We need to take effective measures to rob the dealers of their markets and the only way that we can do that is by supplying addicts through the medical profession, through prescription. We cannot afford to be shy about being prepared to do that."

He said: "It is far better they are going to a doctor, or going to a chemist and are getting their script [prescription] than turning tricks as a prostitute or robbing their mates."

Mr Ainsworth said his departure from the frontbenches now gave him the freedom to express his view that the "war on drugs has been nothing short of a disaster".

He will tell MPs today: "Prohibition has failed to protect us. Leaving the drugs market in the hands of criminals causes huge and unnecessary harm to individuals, communities and entire countries, with the poor the hardest hit.

"We spend billions of pounds without preventing the wide availability of drugs. It is time to replace our failed war on drugs with a strict system of legal regulation, to make the world a safer, healthier place, especially for our children. We must take the trade away from organised criminals and hand it to the control of doctors and pharmacists."

He will also say: "Politicians and the media need to engage in a genuine and grown-up debate about alternatives to prohibition."

Inside Politics newsletter The latest news on Brexit, politics and beyond direct to your inbox Enter your email address Continue Continue Please enter an email address Email address is invalid Fill out this field Email address is invalid Email already exists. Log in to update your newsletter preferences Register with your social account or click here to log in I would like to receive updates on politics every morning by email Update newsletter preferences

Mr Ainsworth said he had seen the way that the heroin trade partly funded the insurgency in Afghanistan. He said: "Bombs and bullets and the wherewithal to produce IEDs [improved explosive devices] are bought by funds supplied by international drugs."

He said the massive number of foreign troops in Helmand had not been able to stamp out the heroin trade, so it was time to consider the alternative of "taking the market away". Mr Ainsworth received cross-party backing for his call for a fresh look at the current drug strategy.

Peter Lilley, the former Tory deputy leader, said he favoured legalising cannabis, while continuing the ban on hard drugs. But he added: "I support Bob Ainsworth's sensible call for a proper, evidence-based review, comparing the pros and cons of the current prohibitionist approach, with all the alternatives, including wider decriminalisation, and legal regulation."

The Labour MP Paul Flynn said: "This could be a turning point in the failing UK 'war on drugs'."

The call met with a stinging retort from fellow Labour MP John Mann, who carried out an inquiry into hard drug use in his Bassetlaw constituency while Mr Ainsworth was drugs minister.

"He didn't know what he was talking about when I met him with my constituents during my heroin inquiry and he doesn't know what he's talking about now," he said.

The Labour leadership was swift to distance itself from Mr Ainsworth's ideas.

"Bob's views do not reflect Ed's views, the party's view or indeed the view of the vast majority of the public," a spokeswoman for Ed Miliband said.

A party source described the legalisation proposal as "extremely irresponsible".

"I don't know what he was thinking," they said.