From Supplement to CAP413:
ILS Phraseology (UK only)
Due to procedure design, airspace complexity and traffic density, along with lessons learned from flight safety related incidents and occurrences, the ICAO phrase ‘Cleared ILS approach’ is not routinely used in the UK. Instead, the UK has enhanced safety by adopting unambiguous phraseology that includes a positive descent instruction to ensure that descent is initiated only when it is safe to do so. ‘Cleared ILS approach’ may introduce an element of uncertainty as to when descent will be initiated because the pilot may descend to the final approach point altitude (platform height) at any time after receiving this clearance. To ensure that descent will only commence when the aircraft is clear of other traffic patterns, such as helicopter routes and adjacent aerodromes’ procedures, radar controllers will normally use the
UK phrase: ‘Report established on the localiser.’ Once established, you will then be given clearance to ‘Descend on the ILS.’ In busy RTF environments, the phraseology may be combined to: ‘When established on the localiser, descend on the ILS.’