Research by the company found that 15 per cent of motorists have made changes to their vehicles in some way, with Norwich found to the place where the act is most common.
Allan Burns, head of Tesco Car Insurance, said that while it was good that many people were "expressing themselves", they need to talk to their provider about the changes.
He added that those who add security measures to their vehicles could also lower the cost of their premiums.
The Association of British Insurers recently urged motorists to shop around when looking for car insurance.
Malcolm Tarling, the spokesperson for the body, recently stated that drivers based in the UK could make a "significant saving" by shopping around for the best deals.
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