Can somebody help me understand this door chime wiring?

I have this inside an old door chime which seems redundant. (UK)

I plan to decommission this door chime, but would like to understand the wiring first. Particularly if it is connected to the mains somewhere.

These wires runs deep into the house and I can't trace the end of them. There were batteries inside too, but they were flat and show signs of leaking.

I can't get any voltage from them with my multimeter (but as I said, bell is dead anyway). What would they likely run to? What does the colour coding mean?