Information is inaccurate or nonexistent, says NU by Shirley Kumar and Tristan O'Carroll
Flood data needed to produce detailed maps is "inaccurate or does not exist at all," said Norwich Union (NU) special projects manager Jill Bolton.
Bolton, who is responsible for producing accurate mapping nationwide, said troubles with finding accurate information has delayed their project by at least six months.
NU, which paid out £200m in claims following floods in 2000, has invested around £3m to produce an accurate digital mapping system to assess the true risk for a property.
But so far the insurance giant - with 89 catchments areas to map - has managed to roll out information based on only a tiny area in Wales using its aerial radar technique and current flood data.
Bolton said: "We are about six months behind schedule because of the lack of information, but it is a complicated system and ours will be the most accurate in the end."
NU says more than 200,000 policyholders will eventually see their premium rates fall when the mapping is complete. Bolton said: "Our mapping will show whether a house is on top of a hill or at the bottom, so we do not blight all homes with the same postcodes."
There has been a year's delay from NU map supplier Intermap - as map experts were called to work for the US government's military operations.
It is also waiting for flood experts to correct more than 200 errors in the engineer's bible, the Flood Estimation Handbook.
The flaws emerged last month when the insurer cross-referenced the handbook with Ordnance Survey maps and its own Geographical Information System data.
The public sector insurer issued the warning as it released new figures that raised concerns over local authorities' risk management procedures.
The new Defra formula means funding for flood defence schemes will be allocated on a risk-defined basis.
The figures showed that poor risk management led to a 50% increase in the annual cost of flood damages, to £22.5m last year.