The tests revealed that an impact of just 6mph can write off a car.
The front and rear of 10 popular new cars were crash tested at the Motor Insurance Repair Research Centre to assess their bumper performance.
Of the 20 tested, only one was deemed to be good, one was acceptable, seven were rated marginal and 11 poor.
However, a spokesman for Suzuki – the Suzuki Swift was highly criticised for its performance – has asked Thatcham to provide more details of how the tests were carried out and how the repair costs were calculated.
“The Swift is one of the safest small cars on the market. It achieved three stars for pedestrian safety in the EuroNCAP test,” he said.
“We are surprised at the report and will be meeting with Thatcham next week.”
Thatcham said the crash tests were conducted under a new international protocol design by The Research Council For Automobile Repairs.
It said they provide conclusive proof that a seemingly inconsequential impact, which on the best performers would cost only a few hundred pounds to repair, are, in the worst performers, costing more than £2,500 in an identical crash test.
On the Suzuki Swift, the combined front and rear repair costs following the 6mph crash tests caused £4,600 worth of damage, which would have written the car off.
“This is a ridiculous state of affairs. If only motorists could see for themselves the limited protection that some bumper systems give their vehicles, they might not buy them,” said Matthew Avery, research manager at Thatcham.