If I have third party insurance on my car, can I drive any other vehicle with the owner's permission?

Normally most comprehensive insurance policies allow the "drive other car with owner's permission" clause because of the higher premiums that you pay for these type of cover. However not all comprehensive car insurance will give you this added benefit. For 3rd party, fire and theft, I doubt they will allow you to drive another car because you pay substantially less and the insurer will not want to extend the cover to some other car and risk making a loss. Nevertheless, you can always check your current insurance policy to see if it allows you to drive another car or you can just call your insurance company and ask them about it.