How to get cheap temporary car insurance in the UK on an international license

Recently I needed to get 12 Days Car insurance to drive a car in the UK on an international Driving License

Services like https://insure2drive.co.uk/ and https://www.sterling-insurance.co.uk/ are made for this , however, for 12 days, they were quoting 400 GBP!!!!!

Marks and Spencer Car Insurance accepts international driving licenses and for a whole year their quote came back to 330GBP

BUT , in the UK there’s usually a 14 day cooling off period for Car Insurance

So I signed up the yearly Marks and Spencer Car Insurance on a Monthly plan , and called them on the 12th day after I’d finished driving to cancel, and 12 days cost me 11GBP!