UK Motor Statistics
According to the RAC car 'parc' (licensed + SORN) has risen from 19 million in 1971 to over 31 million in 2007, an average growth rate of 3% per annum
Department for Transport statistics Table VEH0202 covering the period 1994 to 2018 (these figures exclude SORN vehicles) show a similar upward trend even allowing for a slight wobble following the 2008 financial crisis. (Chart and trendline/equation original graphic by FLUKE)
The continued rising trend is probably due to a combination of increasing UK population and economic affluence and FLUKE predicts that car ownership in the UK (assuming the country continues to be a functional democracy) will exceed 40 million by 2040. Further statistical analysis is required to model the effect of new sales of electric cars, but preliminary work shows the total number of cars correlates reasonably well with the previous 13 years car registrations. Obviously this is a simplification; some cars are written off much earlier and there are cars older than 13 years still on the road. But it illustrates that even an immediate 100% take up of new electric cars would take over a decade to decarbonise personal road transport and for lower take ups, longer still.