You should be aware that if you only have third party insurance you are not covered if your car is stolen or if you have an acciden that is your fault. Some car insurance companies do not offer third party only options.
Every region in the UK is risk assessed by car insurance companies, so even if you are a careful driver you may pay more on your premiums because of where you live.
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.
When making a claim have as many details with you as possible including your policy number and a crime reference number if you have one.