There is an interesting discussion of all these issues in a Home Office published research paper (Tackling the demand for prostitution:
A rapid evidence assessment of the published research literature-available here
External Link/Members OnlyThe conclusion is that the social survey estimates (based on the proportion of men who admit in surveys that they have used prostitutes-and the calculative methods-based on the estimate of the number of prostitutes there are and the number of clients they must see) are at variance. As the report notes (p 3)
"Estimates derived from surveys are lower than those derived
from the numbers of prostitutes and sex transactions. This may
be a consequence of the weaknesses of survey methodology
when applied to this topic. ........ the NATSAL findings suggest a client
population of 175,380, each of whom would need to pay
for sex every single day of the year to account for the total
estimated number of sexual transactions estimated through
calculative methods; clearly, both estimates cannot be accurate."
Now I know some of you are doing your best..and some would like to do it every day...
As an aside-suppose for the sake of argument that there were about 80,000 prostitutes in the UK-and that the average length of working life was five years-and suppose the average starting age was 20 and the life expectancy was 75 , then the number of ex-prostitutes in the UK would be 800,000 -quite a thought.