I have a 1999 Ford focus and am unable to open the rear passenger door?

I have a 1999 Ford focus and am unable to open the rear passenger door from either the inside or the outside of the vehicle I believe the child lock is stuck on but without being able to open the door I am unable to put the key into the lock to turn the safety lock off, is there anything else I am able to try as my car has failed it's MOT due to the door not opening.