The level of pre-registration increased 46% in 16/16 plate volumes during June.
Cap HPI studied 16/16 plate used vehicles advertised on digital platforms.
Philip Nothard (pictured), consumer and retail specialist at Cap HPI, said: “Pre-registered vehicles must be kept for 90 days before sale. A spike in 16/16 plates at the end of June is indicative of activity at the end of March.
“What will be instrumental to the effect on values is how well and how quickly those dealers who are holding high volumes can clear these vehicles.
"There may well be a knock on effect to older cars as a consequence of the price points of nearly-new to compete with the strong new car offers available.”
In June, volumes of 16/16 plate vehicles versus 15/15 at the same time last year, rose by 10%.
Cap HPI declined to provide the volume figures.
The city car segment saw a 66.3% rise in late-plate vehicles when compared to the same point in 2015.
Nothard said: “Aside from the late plate vehicles, the market seems to have stabilised through June and it is likely that there will continue to be demand for the three- to five-year-old stock, with high quality and well specified examples performing well.
"That being said, historically we do tend to see some price erosion take place through July and there may be some easing of retail demand, due to the holiday period and some people may even contemplate how the leave outcome of the referendum will affect them.”
Demand for used vehicles has remained strong through the first quarter of 2016. Research by cap HPI shows used car volumes jumped 13% in the first quarter of 2016 against the same period last year.
A total of 1,975,945 were sold in the first three months of the year, with prices underpinned by strong consumer demand.
The figure is the biggest quarterly increase on record, with a jump of 8 per cent in 2013/4 the previous peak. It is also the biggest quarterly sales figure since 2004, which was the largest on record with 2,005,660.