I always end up getting ripped off by the car rental companies and end up paying around 15-20 quid a day for CDW cover and reducing the insurance excess to zero.
However if you have time, it’s a good idea to look into insurance before hand. However, make sure it’s acceptable by the car hire company.
https://www.which.co.uk/reviews/car-...e-aqd1p9P5n1Rs