How can I insure a car to drive in europe for 5 days?

If the driver already has car insurance in the UK then they need to get a Green Card for France which is proof that the minimum legal requirements for third party liability insurance in any country for which the Green Card is valid are covered by the insured's own motor policy. Most, but not all UK insurers offer this as standard but you need to check before travel. In the case of a new policy, have a look at the insurance tab above and make sure that the cover offered includes a Green Card. As this is minimum insurance only and does not include breakdown, I suggest that you also look at a full European travel insurance that will cover get-you-home and loss of luggage etc.