I think the best approach would maybe be to do bits as and when
appropriate

Though it may complicate matters beyond what is contemplated, if you
plan on
re-running cables then perhaps now is the time to think about any extra
switches or lights that would enhance your house?
The extra cost of three-core-and-earth cable beyond two-core-and-earth
is minimal, hence
when running lighting cable to switches and such I usually install the
former
cable as a contingency for the future.


HTH

Mungo