The crash left customers unable to use their card accounts as well as debit or credit cards when chip-and-pin keypads went offline.

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.

The glitch is understood to be on the Post Office’s back office systems. Supplier Fujitsu is currently testing a fix for the system, to be released shortly.