Goggle & SAS,
The problem with the UK is that we don't have common traffic frequencies for specific areas to achieve the level of situational awareness you probably have in Oz and the US.. There are basically 2 FIR regions that cover the whole of the UK and can give you traffic info, but only the traffic that they are aware of.
For example, imagine you are inbound IFR to an airport in class G for a procedural ILS and you are not high enough to be in controlled airspace before starting the approach. You call up ATC and get cleared for a procedural ILS from overhead a beacon. However there could be traffic crossing through your level, or your approach path that is IMC but still in class G. That traffic could be talking to:
1. The airport you are inbound to (for local traffic info if you are lucky)
2. The FIR controller, who can give flight/traffic info but has no radar.
3. Another airport ATC unit in the vicinity, who may or may not have radar.
4. No one at that particular time, although it would be good airmanship to be in contact with who ever can provide the best service in that area.
So best case scenario is that another ATC unit passes the traffic info to the ATC unit you are working, and worst case scenario is you rely on the trusty old TAS/TCAS, if you have one, and assuming the other guy has his mode C switched on..
BC