<<As Riverboy says: if told "cleared ILS" the crew should maintain the last assigned altitude until intercepting the GP.>>
Everyone knows what they SHOULD do, but it's because some crews DIDN'T that we have this situation in the UK. That said, having worked as a Heathrow Radar Controller for 31 years I had no problem with the R/T phraseology and I never considered it verbose to the extent that spacing was compromised..