Comprehensive insurance is the highest standard level of motor cover. It pays for injury and damage caused to others and also for damage to the policyholder's own vehicle, including in accidents that were the policyholder's fault.
In one line: Comprehensive insurance covers both other people and the policyholder's own car, including fault accidents.
How comprehensive insurance works
Comprehensive cover combines the legally required third party protection with repairs or replacement for the policyholder's own vehicle, plus extras that often include windscreen cover and personal belongings, depending on the insurer.
After a fault collision where the policyholder's car needs 3,500 GBP of repairs and a 400 GBP excess applies, comprehensive insurance pays 3,100 GBP towards those repairs, which a third party policy would not cover at all.
Cover still depends on the policy terms, so exclusions such as driving without a valid MOT can void a claim.
Comprehensive vs third party insurance
Third party insurance is the legal minimum and ignores the policyholder's own car, while comprehensive insurance adds protection for that vehicle too. Comprehensive also tends to come with more built-in benefits.
Holding comprehensive cover on one car can sometimes extend limited third party cover when driving another vehicle, but only if the policy explicitly states this.
Primary source: FCA: Insurance