Insurance giants saw hefty share losses on the London stock market amid fears they face a claims bill of up to £1.5 billion to cover the damage caused by this month's devastating floods.
Professional services firm KPMG estimated a total clean up cost of £5.8 billion, which includes the claims hit to the insurance industry.
More Than owner RSA Insurance and Thistle owner Jardine Lloyd Thompson both fell by 2% on the London Stock Exchange, while Aviva was down 0.5% as Storm Frank threatens to bring more misery to Cumbria and southern and central Scotland.
But most of the nine remaining "severe" flood warnings issued by the Environment Agency for England and Wales - meaning potential loss of life - are centred on York, which was inundated on Boxing Day.
KPMG said it is working with organisations across the North as they respond to the current flooding.
Justin Balcombe, KPMG's UK head of general insurance management consulting, said: "The scale of the flooding over the last few weeks has seen communities across large sections of Northern England, Wales, Scotland and Ireland severely impacted.
"In 2007 when a similar pattern of flooding hit, total insured claims were £3.2 billion; however, we consider that the actual financial impact far exceeded this.
"We are assessing this month's events through a number of economic lenses, resulting in an initial total cost estimate of £5 billion to £5.8 billion."
General insurance leader Mohammad Khan at professional services group PricewaterhouseCoopers (PwC) added that the recent Storms Desmond and Eva would be within most insurance firms large loss expectations for 2015.
But Mr Khan added "any further damage caused by additional rain will impact relevant insurers' year-end profitability".
"It is too early to say whether it causes the 2015 profitability of the household and commercial property business they write to be loss-making," he added.
Howard Archer, economist at IHS Global Insight, said December's flooding could impact growth in the economy by between 0.2% and 0.25%, due to businesses not being able to open, loss of agricultural output and people not being able to get to the shops.
He said: "As the flooding is occurring late on in the fourth quarter, some of this negative impact is likely to occur in the first quarter of 2016."
But he added the economy is expected to see a boost to growth next year from extra construction work when the clear up begins as well as replacement purchase spending.
He said this spending is likely to start in the first three months of next year, and will at least partly offset the hit to activity at the start of the quarter.
KPMG said its £5.8 billion overall clear-up figure also includes around £1 billion of policyholders under insuring their goods and property.
It said this is partly driven by homeowners still feeling the effects of the recession and reducing insurance premium spend and coverage.
The problem also arises as a result of the post Christmas timing, as homeowners will have indirectly increased their content values through presents and food, and while several policies provide for such an uplift, many do not.