Hundreds of thousands of pensioners have been left without access to their weekly allowances after a Post Office IT system crashed yesterday (22 August).
The system failure of the newly-introduced swipe-card system lasted from 10.30am to 3.50pm on one of the busiest days of the week for picking up pensions.
A spokesman for the Post Office said technical teams had created a chronology of the failure but refused to release it because of commercial confidentiality.
"We are still looking into what went wrong. We have a time line of what happened when but we are still getting to the bottom of what caused this unprecedented nationwide failure.
The Post Office spokesman said EDS was responsible for the systems, with EDS subcontracting the work to JP Morgan financial systems. Both parties were working to find the cause of the problem.
He apologised to Post Office staff and to the pensioners affected and said the result of this investigation would be made public.
The failure affected the Electronic Benefits Transfer system. In 2002 the Post Office awarded EDS the contract to supply a system that would allow benefits and pensions to be paid electronically into bank accounts or directly to Post Office accounts for collection.
The government and EDS insist the new swipe-card system is more effective and cheaper to run than the the traditional pension books, which will be phased out next year.
EBT is a component of the £650m Horizon project, run by Fujitsu Services, to allow all benefits to be paid electronically. It followed the failure of the Post Office Pathway system, an IT project for the then Department of Social Security and the Post Office to provide a swipe-card for welfare claimants to receive benefits.
A National Audit Office report said that up to £1bn in taxpayers' money was wasted on the project. Fatal flaws included divided leadership of the project and insufficient attention being spent on the technical details of the system, the report said.