greetings from Downunder.
If you want to clear someone to join the localiser only, and you wish to prevent them descending early, the phrase I would use in this part of the world is "JOIN THE LOCALISER, MAINTAIN 3000FT"
There would probably be an additional "DUE TRAFFIC" or whatever the reason was. Otherwise "CLEARED ILS/DME APPROACH RUNWAY 27" means maintain the current cleared level until able to descend in accordance with the procedure.
As an aside, is the Airfield Elevation published on the chart? How prevalent is the use of QFE in Britain?