There is something in unleaded petrol that makes it go to jelly after a long time (1 or 2 years). If this happens to your car, say goodbye to your pump and lines, and you will need to send the injectors and tank off to be cleaned.
Most duel fuel (petrol/lpg) cars that only use LPG end up unable to run on petrol because of this.
One of the reasons why I didn't want to put my car into storage....