The consumer group identified 302 incidents which prevented customers from making payments in the last nine months of 2018.

The stark findings reveal that serious banking crashes are even more common than previously thought.

Since April of last year, banks have been required to inform the Financial Conduct Authority (FCA) of any major operational or security incident affecting their mobile, internet and telephone services which prevents customers from making or receiving payments.

The most recent figures detail the number of incidents in the final three quarters of 2018.

Using this data, Which? found the average number of major breaches across each of the 30 banks and building societies in its analysis was one a month – with six of the major banks suffering at least one every two weeks.

Barclays reported most major incidents (41), with more than one every week. It was followed by Lloyds Bank (37), Halifax/Bank of Scotland (31), Natwest (26), RBS (21) and Ulster Bank (18).

TSB, where the botched introduction of a new IT system last year caused 1.9 million people to lose access to online banking services, reported 16 incidents.

Jenny Ross, Which? money editor, said: “Our research shows that these major banking glitches – which can cause huge stress and inconvenience to those affected – are even more common than we feared.

“This highlights why it is so important that a regulator is given responsibility to protect cash as a backup when technology fails and to ensure no-one is left behind as digital payments become more common.”