Help on lighting circuit

[piz]

Hello all
I today went to a flat to change a 16mm back box to a 25 mm to fit a dimmer switch all looked ok until I removed the old back box and it was in a copper mineral insulated cable as I understand it I cant connect these 3/4 wires so do I tell the customer she needs a re wire
Expensive dimmer!!! cant isolate it or cap it so do I just leave the breaker off with a notice the cable is like a copper pipe with white chalky powder as the insulation

Help Please

 

[daniel hill]

i am in my second year now at college and we have done at least 20 hours on micc cable in college. i think its a doddle and we use it on all our fire alarm systems and emergency lighting in hospitals in leeds