Prime Minister David Cameron has flatly rejected Nick Clegg's call to end the "unwinnable" war on drugs and explore alternative approaches to cut levels of violence, addiction and crime linked to narcotics.

The Deputy Prime Minister made his call after meeting former guerrillas and victims of violence in Colombia, where the trade in cocaine and other drugs has inflicted massive destruction and thousands of deaths over recent decades.

The Deputy Prime Minister has already warned that Britain was losing the war on drugs and promised in 2012 that the Liberal Democrat manifesto for next year's election will include a commitment to a Royal Commission on the issue. He has asked LibDem Home Office minister Norman Baker to undertake a detailed study of how other countries deal with illegal drugs, including forms of decriminalisation.

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Speaking last night, the Mr Clegg said: "I believe we owe it to both our young people at home and countries abroad... to look at different approaches that could cut the levels of violence, addiction and criminal profit."

Asked whether Mr Cameron agreed with Mr Clegg that policy on drugs needs to be rethought, the Prime Minister's official spokesman replied: "No. The PM's views are well-known and unchanged.

"He thinks that we have the right approach. The Government has a good record in this area, with drug usage at the lowest level since records began."