There were 1,773 dealers with forecourts with over 50 cars in September 2014, compared to 1,367 in September 2013 – a year-on-year rise of almost 30% according to Auto Trader.
Over the same period, the number of dealers with fewer than 21 cars declined from 5,739 to 5,088 – or nearly 13%.
Nick King, research director at Auto Trader, said: "It’s a trend that we think is driven in part by an uptake in digital marketing and forecourt management tools.
"Greater use of intelligence and insight to drive their business forwards means dealerships can increase scale, without increasing either physical presence or headcount."
Auto Trader added that the number of cars listed on its site grew 14% year-on-year in September, to 443,548.