Norwich Union is the UK's biggest home insurer

The firm said the June floods and storms back in January had cost it �235m, while July's floods would contribute a further �165m.

Aviva made the announcement as it reported an 8% fall in group profit for the six months to 30 June, down to �1.56bn from �1.7bn a year earlier.

It said the floods in June and July were the worst "in living memory".

'US growth'

Aviva said it was now looking at increasing premiums at Norwich Union by an average of 10%, but said the rise was not solely a direct result of the floods.

Profits at its Norwich Union unit slide by 50% from a year earlier to �284m in the first half of the year.

However, the weakness in its general insurance business was offset by "excellent growth" in life and pensions, with record half-year sales in both the UK, and particularly, the US.

"Overall, Aviva has performed well in the first half of 2007," said chief executive Andrew Moss.

"Substantial weather-related losses in the UK have been countered by strong growth across our life and asset management businesses.

"The US has continued to be our star performer."