Posted By Glyn Atkinson
If my understanding is correct, the journey to work and back at the start and finish of the normal day are covered by the driver's personal car insurance.

- any other work related journeys using a private car should be done under business insurance, (B1, B2 classes, depending on work being done) as the driver will be undertaking work during an attendance at work period - eg having clocked on, for instance.

Things that companies would need to assess would include : -

The roadworthiness of the car used - correct insurance, tax, MOT,
Responsibility for repairs in any accident situation,
Driver skills in various road situations,
Would there be passengers, and hence, potential third party compensation claims travelling in the vehicle?
Is a passenger insured to drive the vehicle if the main driver falls ill en route?
Suitable rest periods while travelling between sites,
Working time regulations standards to uphold etc.

This is just a starter review without going into any travel risk assessments, driver's health etc.