CRISS
below is an extract from the CAP 413 RT Manual.
1.2
Level Reporting
1.2.1 Only basic level instructions are detailed in this Chapter. More comprehensive phrases are contained in subsequent Chapters in the context in which they are most commonly used.
1.2.2 The precise phraseology used in the transmission and acknowledgement of climb and descent clearances will vary, depending upon the circumstances, traffic density and nature of the flight operations.
1.2.3 However, care must be taken to ensure that misunderstandings are not generated as a consequence of the phraseology employed during these phases of flight. For example, levels may be reported as altitude, height or flight levels according to the phase of flight and the altimeter setting. Therefore,when passing level messages, the following conventions apply:
a) The word 'to' is to be omitted from messages relating to FLIGHT LEVELS.
b) All messages relating to an aircraft’s climb or descent to a HEIGHT or ALTITUDE employ the word 'to' followed immediately by the word HEIGHT or ALTITUDE.
Furthermore, the initial message in any such RTF exchange will also include the appropriate QFE or QNH.
This was introduced in the UK a few years ago and is certainly picked up by UCEs if not adhered to