Flash flooding has caused damage estimated at £15m throughout pockets of the north of England.
The market town of Helmsley was at the epicentre of the damage but was not on Norwich Union's flood map. A spokeswoman said: "Our map is based on river flooding, but Helmsley was not viewed as high risk - it's not possible to predict the impact of flash flooding."
The weather, which apart from floods included hail and severe electrical storms, killed livestock and wrecked homes.
Mike Bond, team leader at loss adjuster Ashworth Mairs was on the scene. "There were 5.43 inches of rain in three hours and 15 minutes - it was horrendous. Roads have been washed away - there was no warning."
Mike Jones, director of adjuster Cunningham Lindsey, said: "It is probable a number of people affected will need to be moved to temporary accommodation. We are currently being supplied with lists of policyholder names and are sending adjusters to knock on doors."
He added that Whitley Bay, some 70 miles away, "had also suffered a significant spike in flood claims".
