MaxReheat:
If you readback 'the ICAO words' I will have to correct you and insist on a readback of the the instruction you were given, as there is a difference.
'cleared for ILS approach' implies that you can descend straight away to the level at which the ILS procedure starts (in the case of LHR, 2500').
With the new UK phraseology you must maintain the last assigned level until intercepting the localiser, then descend. This is to ensure separation from other traffic below you.
Perhaps better phraseology for the UK would have been 'when established on the localiser descend on the glidepath'.