The magazine, which provides employment for the homeless, complained that its streetsellers had been targeted by activists campaigning against Covance, a clinical testing company.

Its management said it was believed that abusive e-mails sent to random members of staff, a burglary and suspicious attacks on buildings over the past few weeks are part of the same campaign.

The latest incident took place when a vendor was selling copies of the magazine in Liverpool city centre. He was approached by an activist who shouted abuse and then punched him in the face.

Covance had placed advertisements in the magazine for several years targeting the mainly young readership to recruit volunteers for clinical drug trials. In recent weeks activists campaigning against Covance have highlighted what they describe as The Big Issue’s “hypocrisy”.

One website for a group calling itself The Covance Campaign read: “The Big Issue have recently printed an article regarding the relevance of animal testing and the fraudulent results gained. So after this, as strange as it seems, The Big Issue are willing to advertise for the vivisection company Covance.”

Richard Brown, managing director of The Big Issue in the North, said that the magazine had no option but to withdraw the advertisements because they could not put the safety of vendors at risk.

He said: “This is a horrific incident and one that we are not taking lightly. We will not put the safety of our vendors at risk and feel we have no option other than to stop running the Covance adverts in the magazine.

“We believe this is a wider campaign to terrorise The Big Issue in the North. Staff have been bombarded with viral e-mails and there have been suspicious attacks on buildings in the last week, including damage to a window, a burglary and a suspicious breakdown of the IT network. Picking on vulnerable people to get what you want is despicable.”

The magazine has reported the assault to Merseyside Police.

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