Tesco has urged the government to change its policy over unpaid workers, after finding itself at the centre of a row over complaints of low wages and allegations of “slave labour”.

A Westminster branch of Tesco was besieged by protestors at the weekend, with police called to deal with a dozen right-to-work campaigners who had forced the shop to close to customers.

A string of companies, including rival Sainsbury’s, have already pulled out of the government’s under-fire ‘workfare’ scheme, which protestors claim lets companies take on staff at little or no cost, with no guarantee of a job at the end of the placement.

Tesco bore the brunt of anger after a job ad for one of its positions was advertised as a permanent unpaid position – which it claims was the result of a mistake by job centre staff.

“Jobcentre Plus wrongly advertised a short work experience placement at Tesco as a permanent, unpaid job,” said a Tesco spokesperson.

“This has resulted in widespread misunderstanding of our position. Tesco has been working in partnership with Jobcentre Plus for many months to offer work experience opportunities lasting up to four weeks for young unemployed people who are struggling to find jobs.

“No-one is under any obligation to take part in the scheme and Jobcentre Plus has assured us that all of those who have come to Tesco have done so as volunteers. Tesco would not take part in any mandatory scheme. This is all about helping young people who want to find a job.”

Tesco said it was now calling on ministers to remove threats to dock the benefits of staff working on the placement scheme, claiming it had resulted in misunderstanding from the public.

“Work experience at Tesco should, wherever possible, be a pathway to a paid job with Tesco. That has already been the case for 300 work experience participants with us so far and we hope it will be for many more people,” the spokesperson added.

“We understand the concern that those who stay in the scheme longer than a week risk losing their benefits if they drop out before the end of their placement. We have suggested to the Department of Work & Pensions that, to avoid any misunderstanding about the voluntary nature of the scheme, this threat of losing benefit should be removed.”