I'm looking to modernise a house with old (1950s) wiring.  The original wiring is in conduit, with no separate earth conductor, but amazingly still functions! 

In practical terms, I think the best thing to do is to remove the conduit - it's too small to accommodate cable and its earth continuity is poor - and start again.
There has been some previous attempt at partial re-wiring; TW&E cables are forced into old conduits; this looks very shoddy and compromises cable ratings.

In terms of lighting circuits, the existing arrangement of looping via ceiling roses won't work, since it's intended to install modern recessed downlighters.

I want to avoid having any cable joins or terminal blocks in locations which will be inaccessible.  All terminals need to be accessible for future inspection and test.
(Am happy to pull out a recessed downlighter to check connections on the top).

I am proposing to run a single cable from the consumer unit to a connection box.  From there, a cable for each lighting circuit would run to a switch and then on to the lights.  The junction box would be accessible (with tools).  There would be two such junction boxes, one for each floor, and each would have maybe four or five lighting circuits.

When I mentioned this to a friend (who once worked as an electrician) he asked me if that was allowed and my response was that I can't see where this would be prohibited.  It may be unusual, but I reckon as long as the protection is appropriate there's nothing wrong with this approach.

This leads to a second issue.  It seems that when interconnecting recessed downlighters, some might just run the cable between them on the ceiling, but I think this is poor practice and that the cable needs to be clipped to a joist or run in a conduit along a joist.  Is there a good solution for this that minimises the need to lift floorboards?

Thanks!