Tens of thousands of human being were unable to carry out basic services, such as sending cartons and banking services, as all 11,500 Post Office branches were hurt.
Many old and vulerable people rely on the network for services, such as subsistence and benefit yments.
The Post Office is also vital for to the functions of thousands of organizations.
Amid the disruption customers took to social media to vent their vex.
Twitter user Golds Pharmacy worte: «@PostOffice all computers are down, Cleadon Woodland South Shields. When will they be active? Head auspices phones down?? On a Monday of all days!»
Another user, Jen Thomas annulled: «Been to Queen Street Post Office Notts, group is down. Nothing can be sent; 2.5-3 hour delay, ap rently country-wide»
The Post Office has apologised and said the problem has now been fixed.
A spokesman chance: «We are sorry for any inconvenience or delay caused to customers this morning when our sprigs experienced problems processing customer transactions.
“Services were contact from around 9.00 until just after 10.00 this morning, admitting that some branches were able to continue to serve customers.
«Our immediacy was of course to resolve the issue as quickly as possible and to do this there was a unquestionably short period when all branches were affected.
“We are continuing to watch services to ensure it is business as usual in our branches.»