As off watch says, this has been discussed before (on more than one occasion!).
Like it or not, the UK normal phraseology is different to many other parts of the world.
I think it stems from an incident years ago when a pilot, having been cleared for the approach, descended to MDA as soon as he had captured the localiser. Whilst I have heard it argued that this is a legitimate practice, it does rather cause problems if the controller has something going on below the approaching aircraft (like Heathrow zone heli routes). The UK seems overly touchy (compared to other countries) about this and that is why you get a two stage clearance - and the second, descent, clearance only when the controller is happy - in the UK.