LONDON (Reuters) - Insurers face their biggest UK flood bill in 20 years, with claims set to top $2 billion ($4.12bn) after intense rain left swathes of central, northern and southern England under water.The bill from flooding in recent days across the central counties of Worcestershire, Gloucestershire and Herefordshire is likely to run into hundreds of millions of pounds, an Association of British Insurers (ABI) spokeswoman said.

That comes on top of an estimated bill of $1.5bn pounds from flooding in June that hit central and northern England and caused chaos in the cities of Sheffield and Hull, the ABI said.

"We could see claims in excess of $2bn," the ABI spokeswoman said.

For the time being, insurers are relying on rough estimates of the number and extent of claims to base their assessment of the overall cost.

"Until we have a better estimate of the number of claims we won't have a more specific figure ... That will probably take a few more days, as many people probably haven't even claimed yet," the ABI said.

The flooding, which has hit thousands of homes and businesses, looks set to be at least as damaging as the major UK floods in 1990 that caused an insurance bill of over $2bn.

Apart from the damage to properties caused by the water, thousands of cars have been damaged, while further claims are likely because of electricity cuts after power stations were hit by flooding and by chaos caused to businesses by the weather.