I used to sell insurance. The Man from the Pru.
Most companies would be happy to make a 15% annual return on Motor Insurance.
They work on experience. Statistics.

The absolute minimum motor cover in the UK is (or was in 1980) Public Liability, which covers you for INJURY ONLY claims against you. If you slide your banger up the side of a Roller, you are on your own. (Many reputable companies won't offer this.)
Next level is Third Party, Fire, and Theft, which also covers liability. Covers the other party if it is your fault. Not you.
Top level is Comprehensive. There is also glass cover, which means that if you chip or crack you windscreen, it doesn't come off the excess.
The Excess is an amount that YOU have to pay (first) in any claim.
Your insurance is VOID if the driver is affected by drink or drugs, or the car is not legal, i.e. untaxed or no MOT. This can be a trap!
The insurance is finished if they write the car off. Even if it has only just been paid.
You have to make a decision based on the factors.
My information is well out of date.