Customers have been unable to complete card transactions at the Post Office today after a computer glitch across all branches.
Debit and credit card transactions using Chip-and-PIN pads at branch counters as well as Post Office Card Accounts have been affected, with customers unable to complete transactions or access accounts. The BBC predicts up to 3.3 million Card Account customers could be affected.
In a statement, the Post Office apologised to customers for the computer problem and confirmed its 11,820 branches remained open.
Martin Moran, Post Office commercial director said: "We apologise to customers for any inconvenience. We are making every effort to restore these services as soon as possible."
The Post Office is making "special arrangements" for emergency cash payments to pensioners and benefits claimants that rely on Post Office Card Accounts.
The firm also advised customers could alternatively withdraw cash from any of the Post Office's 2000 ATMs, which have been unaffected by the problem.
The Post Office said further details would be released shortly.
Royal Mail is set to get another CIO, its third in less than 18 months, when former Network Rail corporate development director Catherine Doran takes over the role from 1 September.
UPDATE: A Post Office statement released at 4.30pm today says the technical problems with PIN pads have been solved as of 3.30pm, having been down since branches opened today. The firm says it made 1,000 emergency payments to Post Office Card Account customers during that time.