Demand for new cars fell by 34.9% last month, an automotive industry body said.
Only 145,377 new cars were registered in June compared with 223,421 during the same month in 2019, according to the Society of Motor Manufacturers and Traders (SMMT).
The trade body said the decline reflects uncertain economic confidence and dealerships in Wales and Scotland remaining closed for much of the month due to the coronavirus lockdown.
Nearly 616,000 fewer new cars have been sold in the first six months of 2020 compared with the same point last year.
Year-on-year demand in April and May was down 97.3% and 89.0% respectively, largely due to the pandemic.
SMMT chief executive Mike Hawes said: "While it&rsquo;s welcome to see demand rise above the rock-bottom levels we saw during lockdown, this is not a recovery and barely a restart.
"Many of June&rsquo;s registrations could be attributed to customers finally being able to collect their pre-pandemic orders, and appetite for significant spending remains questionable.
"The Government must boost the economy, help customers feel safer in their jobs and in their spending and give businesses the confidence to invest in their fleets.
"Otherwise it runs the risk of losing billions more in revenue from this critical sector at a time when the public purse needs it more than ever."
This data shows the scale of the challenge facing car dealerships as they begin operating in the UK vehicle market&rsquo;s &lsquo;new normal.
Karen Johnson, head of retail and wholesale at Barclays Corporate Banking, said: "Although it has been just a few weeks since dealers reopened their doors to potential punters, this data shows the scale of the challenge facing car dealerships as they begin operating in the UK vehicle market 'new normal'.
"Whilst some dealers were able to offer click and collect services during lockdown, the expectation was that most people would wait for dealerships to physically open their doors again before looking at purchasing a new car.
"Dealers will now hope that there is a wave of consumer confidence coming down the line, as restrictions on public life begin to be lifted or at the very least will hope that there is some pent-up demand that might result in increased sales, even if only in the short term."