Back-to-work tsar's business has faced nine official investigations

The company belonging to the back-to-work tsar, Emma Harrison, which is being looked at by Thames Valley Police in connection with allegations of fraud by employees, has been investigated nine times since 2005 by the Department for Work and Pensions.

The revelation is the latest embarrassment for David Cameron who personally appointed Ms Harrison.

Ms Harrison's A4e private-sector employment consultancy has previously had to repay public funds five times since it was handed lucrative back-to-work government contracts. This followed allegations of irregularities in the numbers of people it claimed were successfully returned to work.

Out of the nine investigations, there are new allegations that four unearthed evidence that was not taken further through the criminal legal system after money was returned. Four other cases were dismissed as having no case to answer. One led to a criminal conviction.

Four new arrests relating to fraud allegations have been made by Thames Valley Police at the homes of 4Ae employees. Two women and two men were held on 18 January. All four have been bailed, with no charges brought. But the new police probe has brought calls by some MPs for the multi-million pound government contracts awarded to 4Ae to be suspended.

Margaret Hodge, chair of the Commons public accounts select committee, has claimed that the arrests and new figures for the way A4e operates, suggest a potential structural problem in the way the company is run.

She also called on the DWP to explain why the police were not brought in every time new evidence of irregularities were found. The department claims that on the occasions when money was paid back it was up to A4e to take the appropriate action against its employees.

A4e faced further criticism last night when it was claimed that the company forced some jobseekers to work for it unpaid for at least a month.

It was suggested the appointments could represent a conflict of interest.

The placements were revealed in a Freedom of Information answer from the Department of Work and Pensions which said that unemployed people were sent by A4e's Holloway office in North London to work at two more of its offices in the city.

The former Home Secretary, David Blunkett, who has been paid up to £30,000 a year for the last four years as an adviser to A4e, told The Independent earlier this week that the recent attacks on Ms Harrison's company were, "the same story as two years ago when the company took action themselves and informed the DWP rather than wait for any probe".

Criticism of Ms Harrison and her company has grown since it emerged that, although public-sector contracts dominate her business, she paid herself £8.6m last year.

The company is thought to be worth £300m.