In 2023, with household finances stretched, the number of people mainly using cash picked up as it helped them to budget.
That number fell last year, but campaigners say notes and coins must remain part of the mix for consumers.
"While the number of people relying on cash continues to fall, we know that those who do are often on lower incomes or the more vulnerable," said Adrian Roberts, deputy chief executive of Link, which oversees cash access and the ATM network.
"We must not sleepwalk into a digital-only society before everyone is ready."
He said there were also questions over resilience for a digital-only payments system, such as the back-up options during a widespread power outage.
MPs on the Treasury Committee recently said that shops and services may have to be forced to accept cash in the future to help protect vulnerable people who rely on it.
Meanwhile, the UK's financial regulator has proposed that banks and card providers set their own limits on contactless card payments or are allowed to remove the current £100 payment limit entirely.
That would make entering a PIN even more of a rarity, as smartphones - with extra in-built security - already have no limit on contactless payments via a digital wallet.