If it goes back to non-UK factory defaults then it sounds like it has been customised. The Web / SSH interface doesn't provide a way to replace this base config so it's not possible to replace it in that way. These customisation are normally done in warehouse/factory settings rather than in the field.
In the first port of call, the advice is normally to contact the supplier of the equipment (ie typically your ISP)
If you have the password to log into the device after a factory reset then you can change the running configuration and that would retain the settings indefinitely (until another cfg change via WebUI, SSH, until a .rst flash, or a factory reset or update via tr069).
Devices can retrieve configuration updates remotely via tr069. The configuration for this is in the Management > tr069 menu. If that was enabled and registered to a VigorACS server then a configuration change could be pushed to it. If not enabled, then tr069 updates would not be possible.
If you don't have the password, then contact your supplier for advice. A .rst flash etc would just return the unit back to the customised base config and still have the same password.
