Although it's cheaper to have third party fire and theft, if you drive a more expensive car make a comprehensive policy may offer more protection for any damage to your vehicle. Many companies do not allow third party insurance for cars over a specific value for your protection.
If you have previously been banned or currently have lots of penalty points you can still get insurance but most likely at a higher rate.
It's a common misconception that having fully comprehensive insurance means you can drive any car. Unless your insurance states you're allowed to drive other cars then you cannot. when purchasing your next car insurance policy, check to see if you can drive someone else's car.
In some cases if you add a second driver it can cost you more, especially if that driver is young or has a bad driving record. There are many policies, where if the driver you are adding has as good of record as you, may not cost you anymore.
If you wear glasses while driving it's important if your eyesight deteriorates you get a new prescription. You must meet the minimum level eyesight requirements to drive.