I have spoken with some expert in this topic and he said that the test key switch is still required even though if the lights are self-testing type as we need to have some point of isolation of the lights for service or maintenance purposes, unless there is a possibility of isolating them directly from the fuse however, the distribution board must be reachable ideally in the same room/area. 

Isolation can be achieved at the distribution board by operation of the MCB/RCBO.

I am led to understand that isolating at the main mcb is not recommended due to inconveniencing other occupants of the building, and that a test switch is the desirable method.

Yes, that's what I mentioned above but apparently the DB with the designated MCB needs to be somewhere close to the circuit or component being serviced. I am not sure how far or how close though. 

Yes, that's what I mentioned above but apparently the DB with the designated MCB needs to be somewhere close to the circuit or component being serviced. I am not sure how far or how close though.