The Post Office said all 11,820 branches remained open but it brought in emergency measures to ensure pensioners and benefit claimants were able to access money.
The network’s 2,000 cash machines were unaffected but those who could not use their card accounts were able to withdraw a £20 emergency payment.
Customers reported chaos in branches across the country.
One in Wiltshire tweeted: ‘Just been to the post office they are having a nightmare – all chip and pin machines down across entire PO network. Cash only.’
And one postmaster in Bexley, Kent, described dealing with ‘a lot of unhappy customers’.
He said: ‘It was utter madness. We could not get through to the helpline to find out what was happening.’
The Post Office apologised to customers and said the problem, which lasted from opening until 3.30pm, is now fixed.
Commercial director Martin Moran said Wednesday was the ‘quietest day of the week’ for benefits and said about 1,000 emergency payments were made to card account customers.
