True fleet registrations grew 6.5% year-on-year to hit a record high in March, reports Dataforce.
The month followed a flat January and a 4.8% growth in February.
The top three brands remained unchanged with Vauxhall in the lead followed by Ford and Volkswagen.
BMW was the seventh best-selling brand but had the most growth, with a 50.3% increase.
Toyota was ninth but grew 37.7% to give it a market share of 4.1% - its best result since September 2014.
March also saw the share of alternatively-fuelled vehicles hit a new high, with a true fleet share of 4.9%.
Dataforce said since rates for electric car grants changed by the end of the UK tax year, anticipated purchases may have contributed to this spike.
The company's data shows that true fleet registrations were up by an average 6.8% in Europe.
France saw the largest year-on-year increase, of 15.4%, with the Spanish market growing 8.3%.