Immobiliser problem Peugeot 106 xn 1996 P reg?

I have a problem with my immobiliser on my Peugeot 106 XN 1996. I tried to start the car and there was no power at all. Checked the battery and it was flat, and it was new battery so i exchanged it. Brought it home attatched new battery and now there is a problem with the immobiliser as when i turn on the ignition both the red and green light are permanently on and i can start the car. i am uncomfortable with this as it is a security risk and i wondered if anyone could help. Is there a way to reset it or does it need replacing?