Whiplash injury insurance claims have continued to climb despite a drop in road accident injuries, a study has shown.
The increase has cost the insurance industry an estimated £400m, according to industry body the Institute and Faculty of Actuaries (IFA).
Birmingham has 11 of the 20 worst districts for making third party injury (TPI) claims, according to the report.
The IFA blames the rise partially on claims management companies.
Its third annual report collates and analyses data from across the motor insurance industry for last year.
It shows a marked discrepancy between police data for road accident injuries since 2006 and the number of injury claims made to insurers.
The group's chairman David Brown said: "All of the updated data that we have collated supports the conclusion that claims management companies have had a marked effect on the number of small injury, whiplash-like, claims.
"This increase in claims has cost the insurance industry what we estimate to be £400m, but despite this the average cost of a UK motor insurance policy is decreasing.
"This is good news for the consumer, but it does raise the question of how sustainable this is for insurers."
The report also lists the average size of a small TPI claim for the first time as £8,400.
The IFA said there was a 20% decrease in the number of injuries reported to the police in accidents between 2006 and 2011, but a 40% jump in the number of TPI claims over the same period.
The figures support the view that claims were driven by "a change in claiming behaviour rather than a change in the underlying risk".
The study also shows that the North West was a claims hotspot, with Scotland the lowest ratio of TPI claims to third party damage claims of anywhere in the UK.