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Hundreds of millions of pounds a year in tax would be raised if cannabis was legalised, a leaked government report has found.

A decision to relax laws on the Class- B drug would also cut huge costs currently faced by police and prisons.

It comes after MPs last night debated whether to change the law following a petition calling for the drug to be legalised which had more than 220,000 signatures.

Now the internal Treasury report said relaxing cannabis laws would "generate notable tax revenue" and "lead to overall savings to the criminal justice system".

Mirror Online has looked through the analysis, ordered earlier this year by Lib Dem Nick Clegg when he was Deputy PM - see our full story here.

(Image: Daily Mirror / Rowan Griffiths)

Despite this, the government has said it does not plan to relax the law.

The Liberal Democrats have been calling for a debate on the cannabis laws.

The party's health spokesman Norman Lamb said: "The whole debate has shifted dramatically now... as we see state after state starting this debate, with many states in the US deciding to establish legalised regulated markets.

(Image: Getty)

"And of course the basic principle it seems to me is, do you put a potentially dangerous product into the hands of criminals who have no interest in your welfare at all or do you seek to regulate it? "

"And I think in terms of public health protection of individuals and avoiding the ludicrous criminalisation of so many young people, a legalised regulated market makes a lot of sense."

About 2.2 million people in the UK used cannabis last year.