By ITV News Deputy Political Editor Chris Ship

Liberal Democrat leader Nick Clegg will tomorrow make a manifesto commitment on the controversial subject of drugs use.

He will commit his party to abolishing prison sentences for the possession of drugs - even Class A drugs like heroin and cocaine - in England and Wales.

The Lib Dems say 1,000 people a year are jailed for possession of drugs for their own personal use.

Half of those are for using cannabis, a Class B drug. The cost is estimated at £5 million.

The announcement has been made by Mr Clegg in an interview with The Sun newspaper tonight.

At the moment, we are doing an utterly senseless thing - chucking the people who need treatment behind bars so they simply become even more vulnerable to the criminal gangs who exploited them in the first place. Nick Clegg

This is a Lib Dem commitment for the next election, not a change in coalition policy.

A Conservative Cabinet minister told me this evening that there wouldn't be any changes in their party's policy towards drugs before the election.

But the Lib Dems have succeeded in securing a comparative study of international practice into drugs policy, which is currently underway at the Home Office.

The Government is looking at drugs policies in 10 other countries including Portugal, where they have abolished criminal penalties for personal possession, and Colorado in the US, where they have legalised the recreational use of cannabis in designated places.

The sale of marijuana is now a booming industry in the US state of Colorado. Credit: ITV News

The Lib Dems say the UK should approach its drug problem as a health issue rather than a law and order issue.

Many people, however, will strongly disagree.