The year-to-date performance, however, was much stronger, with registrations up by more than 19% when compared to the same point last year.
July's performance was hindered by a small drop in vans, although larger vans and trucks continued to perform strongly.
Mike Hawes, SMMT chief executive, describes it as "a more sedate July, underpinned by a slight fall in van registrations".
He explains: "This is not surprising, given a particularly big uplift in the same month last year on the back of the launch of several new key models. Demand is still at a very high level, with year-to-date van registrations up 17% as confident businesses continue to invest in their fleets and capitalise on the ongoing trend for home deliveries.
"Registrations of trucks, meanwhile, saw another robust month in line with the sector's performance in the year so far. Once again, the principal gains were made by the heavier vehicles in each market segment."
July's star performer was rigids (3.5 to 6 tonnes), up by more than 76% on the same month last year.