OK, I am too busy to try to find the reference, & thus I will give in, and apologise & say that I can't find the reference to limit the use of split con, but I thought it had come in recently with the last red or green books.
SORRY, it looks like I was wrong, as my memory has failed me, again.
I only have the latest book in electronic format to run a search on, but, if it came in on the red it should still be there.
So, I'll say I was wrong to say it CAN'T be used, but, I will not back down on it being treated as flex, as it does not have an earthed outer, thus it cannot be used in the same manner as SWA.
SO, if you are going to use it in an area where an earthed outer is required to negate RCD protection for example, then you can't, as the N cores are wrapped around under the sheath and are still classed as live conductors, so you can't bury it in walls for example and say that you don't need an RCD in the same way you can with conventional SWA.
The N cores do not have an earthed outer to protect them.
IF I can find the reference(s) I was hoping to, IF I ever have time, I will try, to remember to post it/them.
Sorry.