There is no doubt that any census is going to vastly underestimate the numbers of men who punt as most will not admit it, especially if married, and there are a wide range of confounding factors depending on the population sample taken. This might also skew the age statistic and my impression from talking to escorts and parties etc is that the average age is still 40-50. The percentage of men who punt is very likely to be way above the figure of 10% given in the survey. You can work out the number of punters very roughly from the numbers of escorts - although the number of escorts will also be underestimated and errors will have a much larger effect on our estimate of punter numbers and will very likely give us an greater underestimate of punters as each escort will see more punters in a year than the other way round.
In a census in 2001 it was estimated by the government health agencies that there were 100,000 escorts working in the UK although this is likely to be an underestimate as people are not always likely to admit to being an escort and numbers were obtained from GUM clinics, and it was assumed all escorts register with a GUM clinic. Since then the internet has taken off and we have had a large influx of eastern Europeans so I think it is reasonable to assume this has increased so let's say there are around 110,000.
Escorts see varying numbers of punters per day with some street girls and agency girls seeing up to 20 a day and some working part time and only seeing only one or two a week. If we assume an average of 2 per day 5 days a week (again likely to be an underestimate as some work 7 days a week and most I know see 3 or 4 a day at least) that is 10 punters a week. Allowing for 4 weeks off a year that is 480 clients per escort x 110,000 escorts = 52,800,000 punts per year taking place.
The population of the UK is 65,000,000 of which 32,500,000 are men. The vast majority of punters are aged between 25 and 65, a forty year span. Since the average life expectancy of men in the UK is 79,2 years (say 80) then there are approximately 16,250,000 men of punting age.
Next question is how often on average do punters visit escorts? There will be some who punt twice a week but I suspect the vast majority cannot afford this in time or cash. Some will punt once and never again and some will punt regularly but less frequently, say every 2 to 3 months. If we plump for an average of once every month that is 12 punts per year for each punter and there are a total of 52,800,000 punts taking place so that gives a total of 4,400,000 punters which is just over 27% of all men of punting age. (52,800,000/12)
These figures are necessarily very broad estimates but not, I think, ridiculously far of the mark. However this figure assumes that all 27% of men of punting age are punting regularly once a month and every month for forty years from 25 to 65 years of age, which is obviously bonkers so the actual percentage of men who actually actively punting must be considerably higher. I.e. if men only punt for half that time on average (20 years) then there must be twice as many actively punting to make up the total number of punts i.e. 54% of men, and the number of men who have punted at some time in the past but no longer punt must be added to this to give the total number who have ever punted.
However you play with the figures the total percentage of men that punt at some time in their life is quite significant and probably accounts for the majority of men. If the average escort sees 3 a day (15 per week) instead of 2 this translates to 40.6% of men actively punting monthly for 40 years or 81.2% actively punting monthly for 20 years.
Either way it is way above 10% of men who have punted at some time in their life. Food for thought!