ils clearance

[BrATCO]

Why should there be a difference between horizontal and vertical clearances ?
When pilots are vectored, they don't turn on localizer before being cleared for localizer.
When they are cleared for 3000', why should they descend lower before being cleared for ILS APP, when they hit the GS, once established on localizer ?

I'm not up to date about APP anymore, but I seem to remember I used to deal with ILS approaches in a sequence of 3 messages :

- "Descend 3000' (or 2000'), QNH xxxx"
- "Turn right/left heading yyy to intercept localizer RWY XX" (no mention of QNH)
In regard of the position, I could concatenate these first two messages in one. In this case, I would add : ", report established on the localizer"

Procedure was to aim localizer interception at least 30 secs before GS interception.
Once established,
- "Cleared ILS approach RWY XX, QNH xxxx."
Because of terrain and because I worked crossed runways, some of the approaches including circling, I wouldn't clear for ILS final before established on localizer.

I don't remember I had any problem with this procedure.

I reckon pilots knew then that they shouldn't descend below cleared altitude before being established on localizer AND glide AND cleared for ILS approach.
I thought it was worldwide procedure among pilots.