These are the admittedly somewhat disparate pieces of information gleaned from separate sources that the question arose from.
According to The living wage foundation the real cost of living in the UK is £9 an hour.
Assuming a 37 hour week this comes to £17,375 a year.
According to the OECD half those in the UK between 35 & 44 have incomes (not necessarily from earnings) of £17,000 or less.
From the OECD link provided tab through to the third page (selecting the age range & nation as you go), then drag the marker on the ring around to the 17,000 GBP point & tab on through to "Where your household stands: In reality"
Put together those statements would seem to suggest half or more of the UK population may not be being paid enough to do much more than subsist (it doesn't but the question stands).
Though it should be noted that the OECD figures are after tax & I believe that the Living Wage Foundation's figures are pre-tax, also that the OECD sight compares like with like, results from one set of circumstances can't be used to extrapolate average results for the whole population.
Some discussion on the validity of the information provided is OK of course but the real question is what do current economic models predict as the outcomes for an economy with a disparity like this?