New and used car market in the UK
The total market size for new and used vehicles in the UK is just over $165 billion. I've added that information to your spreadsheet, along with the average price for a new and used vehicle and the number of new and used vehicles sold in the UK in 2017. Read on for a few additional notes!
Figures for new and used car sales and for the average used car price were readily available from British media and auto industry sources. I did have to triangulate the average new car price -- I averaged the prices of the top models in three car categories to arrive at that figure.
There were 2.54 million new cars sold in the UK in 2017. Based on the average price of the Ford Fiesta, the Volkswagen Golf, and the Nissan Qashqai, I've estimated the average price of a new car in the UK is around $23,077.
As of November 2017 (the most up-to-date figure I could find), there were 6,338,188 used cars sold in the UK that year at an average price of around $16,794.
Altogether, the UK market for new and used cars was worth $165,059,109,272 in 2017 ((2,540,000 x $23,077) + (6,338,188 x $16,794)).
In 2017, the UK saw 2.54 million new car sales (at an average price of around $23,000) and just over 6.3 million used car sales (at an average price of around $16,000). All told, the UK's new and used car market was worth just over $165 billion that year. I've added all of this information to the UK section of your spreadsheet.