Liberalised drug laws should be introduced to legalise the widespread use of cannabis to relieve symptoms of certain medical conditions, including the side effects of chemotherapy, the drugs minister Norman Baker will say.

Amid concerns that "credible people" are having to break the law to secure the only substance that can help to relieve their condition, Baker is writing to the health secretary, Jeremy Hunt, to call for a review of the medicinal properties of cannabis.

The intervention by the Liberal Democrat minister highlighted differences within the coalition as it became clear last night the Department of Health has no plans to change the law. The Tories take a more cautious approach to drugs, prompting Nick Clegg to criticise his coalition partners last year for refusing to look "imaginatively" at drug laws. The deputy prime minister said earlier this month the Lib Dem general election manifesto would include a pledge to end imprisonment for possession of drugs for personal use.

In his letter to Hunt, Baker will say current laws for the use of cannabis are highly restrictive. The cannabis-based drug Sativex, which can be used to help relieve the symptoms of multiple sclerosis, can be prescribed by GPs, though it is highly expensive.

Baker wants to liberalise the use of cannabis to allow it to be used to relieve the symptoms of conditions such as the side effects of chemotherapy and HIV/Aids treatments and Crohn's disease.

The drugs minister said: "I think it is time to reconsider medicinal properties of cannabis, given what I've learned in my role as a minister. I've seen more and more evidence that cannabis can provide genuine medical benefits to treat a number of conditions. There is a growing body of research that shows the medical properties of chemical components of cannabis. I am uncomfortable that there are credible people I have met who tell me that cannabis is the only substance that helps relieve their condition but not only are they stopped from accessing it officially but have to break the law to help their health.

"Other countries recognise that cannabis does have medicinal benefit and we need to look again at this to help people who are ill. This is a quite separate matter from the recreational use of cannabis which is not at issue here."

Baker spoke after United Patients Alliance, which campaigns for the legalisation of cannabis for medical use, held a meeting in Brighton last month which featured a series of sufferers who admitted they broke the law to relieve their condition.

Alex Baker, 23, a musician from Brighton, said that smoking cannabis helped him complete his exams after he was diagnosed with Chrohn's disease. He said: "I worked out that smoking cannabis meant I could control my bowel for a few hours. So I smoked before all my exams and I got through them. I thank cannabis for that, because I think the pain and the constant toilet trips would have meant not being able to get through a few pages of an exam paper."

Keiron Reeves, 29, who treating severe epilepsy with cannabis oil, said: "I feel much healthier and more confident in addressing everyday tasks like washing, shopping, tidying, all those things most people take for granted. I owe this all to cannabis. I need this medicine to live a better quality of life. I don't feel that I should have to risk a criminal record just for trying to have a normal life."

Baker added: "Obviously we have to do this right, we need to ensure that the proper medical processes are applied. But I've always said that we should follow the evidence, even if that takes us to uncomfortable areas of policy-making."The Baker proposals received short shrift. A government spokesman said: "This government has no plans to legalise cannabis or to soften our approach to its use as a medicine. There is clear scientific and medical evidence that cannabis is a harmful drug which can damage people's mental and physical health.