Over the last year, the main UK banks suffered 265 IT issues across internet, mobile and telephone banking systems which prevented customers accessing their accounts and making payments.

RBS and Santander endured the most IT glitches, racking up 18 incidents each, followed by Barclays (17), Tesco Bank (16) and First Direct (15).

Surprisingly, TSB which has suffered long periods of IT problems reported just six glitches in the past year, a lower number than many of its rivals.

At the other end of the scale, M&S Bank and Starling Bank were glitch-free over the year, according to the analysis of Financial Conduct Authority (FCA) data by Which?.

The campaign group is now calling for the next government to protect the UK’s cash infrastructure in the wake of the IT problems reported. It said banks must ensure their systems are up to scratch particularly as they try to persuade customers to move online.

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Its research revealed 11 million adults (22%) lack the confidence to do basic banking tasks online.

Two-thirds (65%) said they would find it difficult to live their life without access to a bank branch and 8.4 million (17%) said they prefer to bank in branch.

In additon, 94% were concerned about digital connectivity, while 92% were concerned by safety and security online.

Gareth Shaw, head of money at Which?, said: “These findings show the industry is still failing to get to grips with alarmingly frequent banking glitches, which can cause real stress and frustration for millions of people left locked out of their account and struggling to make payments.

“In our nationwide survey, consumers have made it clear that cash is a vital back-up when digital systems fail – so it’s clear the next government should urgently introduce legislation to protect cash for as long as it is needed.”

Stephen Jones, chief executive of UK Finance, the banking trade body,  said: “Operational resilience is crucial in a modern financial system and the industry continues to invest billions to ensure systems – human and digital – are robust and secure. When incidents do occur, firms work around the clock to minimise disruption and get services back up and running as quickly as possible.

“Digital innovation is transforming the way money is managed with 24/7 access to payment systems, increasing the range of day-to-day banking options and providing better back-up for customers if a service is temporarily disrupted.”