Well all I can say is if for whatever reason the ignition thinks the key is in it it wont allow remote locking, whether that's the switch or barrel that does it I've no idea but if the switch is funky change it and see if the problem is still there.
 
Ignition switch didn't change the central locking but car starts better the old ignition switch was massively worn in comparison to the new one.

So whats next on the list to check?

CCM Changed/Tested
Several Remotes Tested
All locks work / no faults
Ignition Switch Replaced
 
I wonder if the antenna wire could be bad, you can buy coaxial cable from the likes of maplins and try changing it, I can't think what else.
 
When I added all the electrics and remote locking I just coiled the wire up under the dash, works fine, the original wire will run up the door pillar.

If everything else is spot on though I can't think what else it could be, definitely the correct frequency remote fobs?