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.

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. 

It's not a requirement, but that's where the discussions with the client come into play for how they envisage the building operating. The key test switch doesn't normally isolate the circuit, just breaks the permanent live to the emergency fittings. For maintenance you'd still need to isolate at the board, but for phased manual testing, distributed key switches are good. Self test does away with that though.