During his visit, the minister was taken to a drugs den by police officers, where two addicts slept amid a debris of needles and squalor.

I was aware that this kind of thing existed but actually to see it in reality was quite a shock

Bob Ainsworth Home Office Minister

Mr Ainsworth said: "I've seen things like that on television but I have never seen them at first hand.

"I was aware that this kind of thing existed but actually to see it in reality was quite a shock."

Since the start of the experiment, 218 people have been officially warned for the possession of cannabis compared with 168 people arrested in the same period of time last year.

But the Metropolitan Police said reliable results would not be available until February.

Hard drugs

The government visit coincided with a meeting between pro-legalisation groups and the all-party Homes Affairs Select Committee.

The MPs were expected to hear arguments in favour of decriminalising all drug use from campaigners including civil rights groups Liberty, Transform and the Legalise Cannabis Alliance.

Bob Ainsworth met officers and residents of Brixton

But Mr Ainsworth was keen to stress that the Government wanted to target more resources at dealing with offences relating to class A drugs.

And he denied the scheme was a step towards the legalisation of cannabis.

He said: "We have a high cannabis use in this country - it is the illegal substance used more than any other.

"Cannabis remains illegal, it will be confiscated and users will be cautioned, they will be committing a criminal offence."

Supporters have suggested that Lambeth could serve as a possible model for reform in other parts of the country.

'Travesty'

Danny Kushlick from drug reform group Transform said the meeting with the Home Affairs Select Committee was a valuable opportunity.

It is our job to...show the committee why so many European states have already decriminalised the possession of all drugs and why Switzerland and Holland are now seeking to legalise the supply of cannabis."

Mr Kushlick said Home Office evidence to the committee had been a "travesty", adding: "Their evidence has manipulated data to support an untenable position."

Downgrading

The Home Office said that in the past six months the rate of class A drug-related offences being dealt with by the courts has risen by 45%.

But last month Home Secretary David Blunkett announced he would consult with the Advisory Council about the possibility of reclassifying cannabis from class B to class C.

That would mean possession of small amounts of cannabis would no longer be an arrestable offence.

Last week the committee also faced a strong rebuke from chairman Chris Mullin MP.

He attacked members' failure to look at the arguments surrounding radical measures, including the legalisation of all drugs.