In a press release accompanying the data, SMMT Chief Executive Mike Hawes said a slowdown was to be expected.
"With the rush to register new cars and avoid VED tax rises before the end of March, as well as fewer selling days due to the later Easter, April was always going to be much slower," he said.
Overall in April, 152,076 cars were registered with fleet purchases for businesses and government agencies accounting for almost 60 percent of new cars.
Hawes said the drop of from March's bumper figure of 170,000 does not suggest a trend.
"It's important to note that the market remains at record levels as customers still see many benefits in purchasing a new car. We therefore expect demand to stabilise over the year as the turbulence created by these tax changes decreases," Hawes added.
The SMMT reported that demand was lower across differing types of buyers with registrations by private buyers, businesses and large fleets falling -28.4%, -21.0% and -12.3% respectively.