HLS has been left without an auditor after Deloitte & Touche severed ties with the company following 10 days of intensive protests against the firm by activist group SHAC and other animal rights sympathisers.

Capital market requirements suggest HLS needs another Big Four firm to take on the audit, but it is thought they are reluctant to put staff at risk of intimidation.

HLS is now a wholly owned subsidiary of Life Sciences Research Inc, which trades on the OTC Bulletin Board in the US. It was forced to trade outside the UK after sustained protests made it difficult to continue its UK listing.

But the Securities and Exchange Commission has said that if a company fails to file audited reports within the allotted time-scale, it would face being delisted from the stock exchange. 'Cases are handled on an individual basis and extensions can be offered, but all reports filed with the SEC have to be audited,' said John Nester, SEC spokesman. He added that once a company is delisted, it no longer has to file its reports.

No one at HLS was available for comment.