You'd have to be more specific as TV viewing figures are only given for a specific program as opposed to the total amount. You could probably get a rough idea if you got the amount of viewers that watched every TV programme in the UK. According to a friend who works in the TV industry there are approximately 20 million licence fee payers in the UK, so I'd guess that would be your answer. Please remember though that most households have more than one TV and according to the UN, the UK has 59.2m people so the amount would possibly be higher than the total amount of licences.