MO says her son lost control of his car on polished cobbles on the approach to a roundabout. Assuming this is a local authority maintained road she should contact the Highways Department and ask: What the required skidding resistance is for the location in question (approaches to roundabouts have specific requirements depending on traffic volume); What the actual skidding resistance of the cobbles is (most highways authorities have their own laboratories for testing skidding resistance using a pendulum tester). If they don't have a value, ask them to justify the use of cobbles (which are notoriously slippery). At the approach to a roundabout, if anything, one might have expected high skid resistance calcinated bauxite chippings (often red), which are stuck to the road with epoxy resin if the traffic volumes and accident record justifies it. If they can't give a sensible answer, make a claim.