Sharecast - Its latest figures showed a rise of 11.6% to reach 132,990 registrations in the month, although the market remained 17.4% below pre-pandemic levels in 2019, when 141,583 units were sold.
Fleet registrations increased 33.1% to 68,537 units, but the number of deliveries to private buyers dropped 5.5% to 61,342 units.
Smaller business fleets accounted for 3,111 registrations, making for a rise of 13.3%.
Petrol-powered cars retained their best-selling status, comprising 58.1% of all registrations, while battery-electric vehicles (BEVs) remained the second-most popular fuel type, with deliveries up by more than half to 20,522 and 15.4% of the market.
Plug-in hybrid vehicles (PHEVs) posted strong growth, up 33.3% with 8,595 registered in the month, while hybrid electric vehicles (HEVs) recorded a 7.7% increase to 15,026 units.
As a result, electrified vehicles accounted for more than one in three registrations in April.
The market had grown by 16.9% in the first four months of 2023, the SMMT said, worth £3.2bn, as supply chain pressures eased.
That led to a positive revision of the quarterly market outlook, with 1.83 million new car registrations expected in 2023, up from the 1.79 million anticipated in January.
The new outlook represented a 13.5% increase - the highest percentage gain since 1983.
However, the SMMT downgraded its expected 2023 market share for BEVs from 19.7% to 18.4%, due to high energy costs and insufficient charging infrastructure, which were anticipated to soften demand.
Its latest outlook for 2024, meanwhile, suggested that 22.6% of new car registrations would be BEVs - a downward revision from the 23.3% forecast in January.
The SMMT called for greater investment in infrastructure, more incentives to encourage purchase, and faster action to accelerate the uptake of zero-emission vehicles ahead of the zero-emission vehicle mandate coming into effect next year.
“The new car market is increasingly bullish, as easing supply chain pressures provide a much-needed boost,” said SMMT chief executive officer Mike Hawes.
“However, the broader economic conditions and chargepoint anxiety are beginning to cast a cloud over the market’s eagerness to adopt zero emission mobility at the scale and pace needed.
“To ensure all drivers can benefit from electric vehicles, we need everyone - government, local authorities, energy companies and charging providers - to accelerate their investment in the transition and bolster consumer confidence in making the switch.”
Reporting by Josh White for Sharecast.com.