Two of the UK's leading household insurers are bracing themselves for a collective flood bill of at least £230 million in the wake of the devastation caused by two weeks of torrential rain lashing northern and central England.

Aviva, the owner of Norwich Union, is expected to bear the lion's share of costs.

It controls about 20 per cent of the home insurance market and is preparing to pay out at least £175 million in claims.

Royal & SunAlliance, the largest commercial insurer and owner of More Than, is anticipating having to pay out insurance claims of about £55 million relating to flood damage.

Aside from two flood incidents in the past five years, most notably in Carlisle in 2005, the past fortnight's events represent the first big floods in 50 years.

Aviva said that it agreed with the Environment Agency that the recent rainfall had been a "once in a 150-year event".

With claims still coming in, the expected cost of insurance claims was Aviva's "current best estimate" and could rise further, a spokesman said.

"It is very early days," a spokesman said. "In some cases, people haven't managed to get back into their properties. it's difficult to know what the scale of this might be. It might keep on raining."

Aviva and RSA are expected to be the first of many household and general insurers to reveal the cost of the flood damage.

The Association of British Insurers said this week that it expected the total insurance bill for the flood damage to reach £1 billion.

Aviva said that since the floods began it had received more than 13,000 claims from customers whose furniture and household goods were lost or destroyed.

It said that its worst-effected areas included Sheffield in the North East of England and Hull in the East, where large areas remain under water.

It also said that claims had been heavy in about 14 other areas, including Rotherham, Doncaster, Cheltenham, Louth and Nottingham.

RSA said that its loss adjusters had arrived on the scene within a matter of hours and were working closely with customers and local councils to facilitate both help and claims processing.

Both insurers emphasised that their profits guidance remained unaffected.

Aviva said that its estimate included projections about claims arising over a 30-day period dating from the beginning of the floods.

Between 80 per cent and 95 per cent of household insurance claims are made within this time.

It hopes to limit the size of the average claim to less than £15,000 and pledged not to blacklist any of its customers over flood claims.

The performance of Aviva's general insurance division in the first half will be "impacted" as a result of the floods, it said, although it is not expected to have to include the costs as an exceptional item.

For the first half last year Aviva made operating profits from general insurance and health of £555 million.

RSA said that it would include the impact in its first-half results.

Aviva shares fell 6p to 762p. RSA was up 0.1p at 150.3p.

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