Door locks

I've searched for this problem but can't find the answer. Fabia 1.9 sdi estate - all the door locks work on the fob except the passenger lock, and that doesn't work on the key either. I suspect there's a relay involved as the flashing red light doesn't work either which to me suggests an electrical problem. The lock works fine if you use the lever inside to open it, and locks OK by manually pushing the button down.

Has anyone had this problem before and is a relay involved? Any hints on a fix? I'm ok with stripping the doors as I've just done the leaks on the rear ones!

thanks