The indication of "Heavy" wake turbulence category is an ICAO requirement and has been for a long time. It is specified in DOC 4444
The idea is base on a number of safety issues.
From a pilot's point of view there are many airspaces where we get no separation from other traffic. Knowing that the ABC123 crossing our track is a heavy gives a good heads up as to possible wake encounter.
Good to see that the UK CAP has finally caught up with international safety measures.
Regards,
DFC