I seriously doubt you would get extended finance for your car. My IP also said "yea, no problems, once the finance is up you can refinance for another car as long as your payments don't change" that didn't happen. The finance company rep I spoke with almost burst out laughing at me once a new credit check was carried out!
Last Payment made 04/12/14. Completion Certificate 25/7/15. IVA company GT. No Issues