A two-year investigation has concluded that a collision at just 10mph could cost more than £4,000 to repair.
Many vehicles fail to offer sufficient protection from a minor collision because of poor design, leading to unnecessarily high amounts of damage.
Thatcham says the failure of many vehicle manufacturers to address the problem is costing British insurers an estimated £250 million per year. This could lead to higher insurance premiums, loss of no claims bonuses and unnecessary inconvenience, it says.
Vehicle repairers are also affected, because vehicles are often needlessly written off, depriving them of much-needed business.
European law requires bumpers to withstand simple pendulum tests, but many cars are designed only to meet these standards and not to cope with real-world prangs.
Crashes involving sports utility vehicles (SUVs) can often result in the larger car riding over the top of the smaller, damaging expensive components behind the bumper.
Matthew Avery, crash laboratory manager at Thatcham, said: ‘Despite outward appearances too many cars on the road do not have sufficient bumper protection.’