Lawyers for shareholders in Interserve, the troubled support services group, have sent the company’s board a letter asking for more information on the accounting irregularities that caused its share price to tumble.

It is understood that law firm Mishcon de Reya sent a letter on behalf of Bob Morton, the former chairman of facilities group MacLellan, which was bought in July by Interserve.

In August Interserve revealed that accounting irregularities had left it with a potential £25m hole. Six staff have been suspended.

The company has postponed its interim results statement, due this week, in order to address the problem, which is thought to date back five years.