It’s not often that a liberal newspaper like The Guardian rails against an organisation like Amnesty International.

But last week the paper ran a stinging editorial questioning the wisdom of the human rights group.

It said Amnesty would make a “serious mistake” if it advocated the decriminalisation of prostitution – a decision the group’s international council will vote on later on Tuesday.

It’s not just The Guardian that is upset. Several women’s groups have got together with a host of big-name actresses – including Meryl Streep, Emma Thompson and Kate Winslet – to criticise Amnesty after a draft of its policy proposal was leaked.

Amnesty’s leaked proposal says decriminalisation would be “based on the human rights principle that consensual sexual conduct between adults is entitled to protection from state interference” so long as violence or child abuse or other illegal behaviour isn’t involved.

Those who favour decriminalisation say it removes the stigma of prostitution and makes it easier for sex workers to go to the police if they need protection from violence.

But there are many who argue that the German experiment has gone badly wrong with very few prostitutes registering and being able to claim benefits. Above all, the number one criticism is that it’s boosted sex tourism and fuelled human trafficking to meet the demand of an expanded market.

Figures on human trafficking and its relationship to prostitution are hard to establish. But one academic study looking at 150 countries argued there was a link between relaxed prostitution laws and increased trafficking rates.