how can i unlock my doors?

I have a year 2000. 3 door fiesta zetec 1.2 and cant unlock either door from outside. I have to open the hatch from outside and climb in through rear, once inside I can unlock doors. Yet when I get out I can lock either door and the central locking works. There are no buttons on my key just an immobilizer. Can anyone help.

Craig
April 2013