We have some quarterly stats from the ONS.
By the end of the quarter the UK workforce consisted of...
Employed: 28.86 million people
Unemployed (but looking for work): 2.45 million
Economically inactive: 8.16 million
The total workforce is therefore around 40 million people. The remaining 20-odd million are either too old or too young to work.
Of the 28m employed people 7m are working for the government, so they're not wealth-producing as such.
So that's 22m workers supporting a population of over 60m
ONS news release