Interserve has been asked by a major shareholder to explain accounting irregularities following the company’s shares losing a fifth of their value.

The firm has suspended six senior employees from its industrial services unit following ‘mis-statement of accounting balances going back at least five years.’

Mishcon de Reya, lawyers for shareholder Bob Morton, have sent a letter demanding information about the irregularities in the firm’s finances.

Morton is the former chairman of MacLellan, a rival support services firm bought by Interserve for £118 million in July. He and other former shareholders in MacLellan are considering claiming compensation for the loss in value of holdings.