Britain is about to see its first ever ad campaign for the legalisation of cannabis.

The advert, which will be featured on the side of a van as it cruises around central London for three days, comes courtesy of the Clear campaign group.

"It really is time that politicians started listening to the electorate and following the evidence on cannabis," leader Peter Reynolds said.

"Present policy actually causes harm and denies access to medicinal cannabis for millions in pain, suffering and disability.

"It puts billions into the hands of organised crime, abandons children to street dealers and promotes dangerous hidden farms that cause fires, blight communities and involve human trafficking.

"In a regulated system we would have age limits, quality control and tens of thousands of new jobs in legitimate businesses."

The 48-sheet poster is emblazoned with the slogan 'Let's Get The Dealers Off The Streets!' and calls on the government to "legalise, regulate and tax the £6 billion cannabis market for a safer, healthier Britain."

The message will be supported by a YouTube commercial.

Clear, a political party which campaigns for the legalised use of medicinal cannabis, is following the advert with a crowdfunding appeal seeking to raise money for a longer campaign.