It is obviously still possible to obtain a "Traffic service" in UK's Class G airspace, where available (there are surprisingly large gaps in LARS coverage).
But it will often be a limited service (or basic only offered) due to a number of reasons; for example:
Poor radar performance.
Radar suppression.
Radar clutter.
Traffic density.
Controller workload.
Controllers on holiday - military radar units are sometimes stood down.
Etc.
So, rely on obtaining an ATC service OCAS is only part of the answer. See and be seen is still paramount in Class G.
I'm lucky enough to be assisted by TCAS but that relies on other aircraft using their transponder if fitted, preferably with ALT/Mode C selected.