Norwich Union (NU) has written new fleet business voraciously over the past month, but stridently denies it has undercut its competitors.
NU intermediary business director Ken Wallace said the insurer was targeting private vehicle fleets, but would consider heavy goods vehicles "in the right circumstances".
"We're also looking to fleet to support our property account," he said.
However, Wallace denied rumours his team was undercutting competitors' prices by up to 80%.
He said there was absolutely no question of NU "buying business in" or failing to underwrite the business correctly.
"Our fleet rates are competitive but are still giving us a good return," he said.
Wallace said NU's blue chip status was bringing it new business, amid concerns about other insurers' financial stability.
"The commercial drive we started in September has continued into October.
"We've done a huge amount of new business and there's no sign it's letting up," he said.