If I hear "cleared for the ILS app" while I am following a published arrival track, I will automatically assume that that means I can descent according to the published altitudes. As Sonnendec suggested, in case of doubt, I would check ATC if that is exactly if that is what they meant, even if I don't think I have to check.
If I'm on radar vectors at 3000' on a final intercept course and I hear "cleared for the ILS" I will assume that I'm automatically cleared to the published G/S intercept alt should it be lower (e.g. 2000'). Again, in case of doubt, I would check with ATC if that is what they meant, even if I don't I think have to.
On the few occasions I fly to Britain, I have noticed that ATC often wants you to report established on the LOC, before issuing the "cleared for approach"
That procedure is a waste of time and bandwidth in my opinion and increases the workload on an otherwise already busy frequency.
Outside the UK if often hear "cleared for the ILS, leave 3000' on the glide slope". That's the ideal short and unambiguous clearance in my opinion.