According to CAP 413-
http://www.caa.co.uk/docs/33/CAP413.PDF Chapter 2-pg 4 section 1.4.4
All six figures shall be used when identifying frequencies irrespective of whether they are 25kHz or 8.33kHz spaced. Exceptionally, when the final two digits of the frequency are both zero, only the first four digits need be given.
I hope this helps!
Best of luck