What is the main source of data that determines the rate for an insurer's private car portfolio?

The primary basis for determining the rate for an insurer's private car portfolio lies in its own past claims history across similar risks. This approach leverages historical data regarding claims filed by policyholders, which reflects the actual loss experience and risk associated with insuring those vehicles.

By analyzing this data, insurers can identify patterns and trends in claims, allowing them to accurately price their policies based on the likelihood of future claims for similar risks. This empirical evidence provides more reliable insight than relying solely on external data sources or industry averages, as it is directly tied to the insurer's own business performance.

While other options may provide useful information, such as competitors' rates or statistical data from the DVLA, they are often not as specific or tailored to the insurer's particular risk profile. The Motor Insurers' Bureau claims experience could offer insights into overall market trends, but again, it does not carry the same weight as an insurer's individual claims history in setting rates.