The Post Office failed to find out why large cash shortfalls occurred at sub-post offices before starting civil and criminal proceedings against sub-postmasters, according to a report by forensic accountants. The report looked into complaints by sub-postmasters of unfair sackings and wrongful convictions caused by flaws in control systems. Concerns were raised by MPs in 2012. The Post Office vehemently denies the report's conclusions. The report also revealed that the Post Office had refused to hand over documents which the accountants felt they needed to investigate properly.  A number of MPs raised concerns that dozens of sub-postmasters had been faced with unexpected demands to pay large shortfalls - and been sacked, sued or prosecuted for theft when they could not pay. Alan Bates, chairman of the Justice for Sub-postmasters Alliance, has previously said problems with the computer system were reported since its introduction more than a decade ago.