UK Finance found that in 2016, cash was exclusively relied upon by 2.7 million people in the UK. Further still, 15.4 billion payments within the country were conducted with cash, making up 40% of all payment and 44% of all consumer transactions. That's a lot. 

Excerpt from Finance UK report

There were 2.9 million consumers who rarely used cash in 2016, representing 6% of the UK’s adult population. People in younger age groups are more likely to be rare cash users than people in older age groups, with more than one in ten of those aged 25-34 making one cash payment each month or no cash payments at all.