How can i fix rear door lock problem on a 2003 astra ?

Hi , can anyone please tell me how i can fix a door lock / latch problem on a 2003 vauxhall astra ? The rear left door has become permanantly locked , i can unlock it neither from the inside or the outside . The cdl plunger in the door does nothing when key operated and is still locked when in the up / unlocked position . I was wondering whether there was a seperate fuse to this door , any help much appreciated , thanks .