I note your statistic refers to "people" and not "adults". Usually, some proportion of the people of any given country are ineligible to receive a drivers licence on the basis of their age. It seems that age is 17 in the UK, although I'm not sure whether that counts as full or provisional until they've got a bit more experience. I'll assume full.
According to https://www.ons.gov.uk/peoplepopulationandcommunity/populati... there's about 1.2% of the people in each age group <17 in England, which means 1.2*17 ~= 20 of the people in the England are ineligible for a drivers licence. So there's only about 6% of people in the England who could have a full drivers licence, but don't. So either they give licences out in the cornflakes at Tescos, or almost the whole adult population of the UK wants a drivers licence.
According to https://www.ons.gov.uk/peoplepopulationandcommunity/populati... there's about 1.2% of the people in each age group <17 in England, which means 1.2*17 ~= 20 of the people in the England are ineligible for a drivers licence. So there's only about 6% of people in the England who could have a full drivers licence, but don't. So either they give licences out in the cornflakes at Tescos, or almost the whole adult population of the UK wants a drivers licence.