At common law, which of the following is NOT a requirement for contribution to arise?

To understand why "common sum insured" is not a requirement for contribution to arise at common law, it's important to define what contribution means in the context of insurance. Contribution is the principle that allows insurers, who are covering the same risk, to share the losses proportionately if a claim occurs.

In cases involving multiple policies issued by different insurers covering the same risk, the principles of contribution dictate that the insurers will settle the claim based on their respective shares of the risk, as long as certain conditions are met: there must be common insurable interest, common subject matter, and common peril that causes the loss.

The requirement for a "common sum insured" is not necessary because insurers do not need to insure the exact same amount or value for a contribution to be valid. Each insurer can provide different sums insured based on the individual policy terms. What matters more in the context of contribution is that the loss relates to the same subject matter and peril, linking all policies together despite possible differences in sum insured. This allows for equitable treatment of claims based on the exposure each insurer has agreed to cover, independent of the total sums insured.