I had a very close encounter with a C172 today, crossing right to left at my altitude. I didn't see it against the white cloud (why are so many aircraft white?) and it could have ended badly. I asked ATC about it and they confirmed there was no target (neither primary nor secondary). I do get a lot of "primary target" advisories from FIS Munich so their system does show primary targets. I wonder why this aircraft was not on the radar.
Maybe it was Mathias Rust? I am all for making transponders mandatory everywhere.
I think there is something cultural about this and I'd like to make a serious point:
In the US, when a controller calls traffic (under flight following for instance) they mean you to see it. If you don't report 'in sight' they are prone to keep calling you back. This may be because of proceedures where the other traffic is held until you report visual, such as in Las Vegas class 'B', but can happen OCAS just the same. In America, traffic calls are meant to be acted on.
In UK, the whole thing feels more like a box ticking exercise with an actual sighting of the traffic being a bonus. I wonder if the relative scarcity of a visual sighting (I see about 50% of the traffic called out in US, but only maybe 25% here) has something to do with the accuracy of those controller call outs? the How many times have you had "12 O'clock, 1 mile, same level opposite direction" and still not seen it? In America, never, but here?
Equally under a 'Basic' service I've had a military helicopter come at me head on out of poor vis and had to dive away seeing clearly into his open door that none of the crew had seen me, all courtesy of their own radar who said nothing. Now maybe according to their bureacratic rules my VFR flight doesn't exist, but their helicopter does and still they did nothing!
Of course, I'm comparing a radar service (for instance, flight following) with a 'Basic Service' (whatever gibberish that is) in UK. But I'm relating to actual traffic calls that have actually happened to me and I'm questioning the accuracy of the controller call outs. We are very fond of taking the blame for everything in GA and I'm seriously puzzled about the amount of invisible traffic on this side of the Atlantic.
In America, traffic calls are meant to be acted on.
Works exactly the same way in Germany. You either report a "in sight" or "looking for traffic" and in the latter case you get updates and finally "traffic no factor" if you don't spot it.
However, both in Germany and the US I have experienced "traffic information not possible due to capacity". That is usually exactly when you need it the most 
You should compare flight following with a traffic service in the UK.
A basic service offers not much more than tieing up radio waves by collecting your call sign and flight details and then throwing it away afterwards. It is NOT a surveillance service.
You should compare flight following with a traffic service in the UK.
Absolutely. That's why I am comparing actual traffic call outs made by ATC, whatever the service. I rarely use Traffic service in UK because, as they say, "refusal can often offend".
Aveling that was an interesting point regarding the UK box ticking scenario. I believe that to be accurate in the UK.
I always, when receiving a service from in transit Information Services, tell them when I am looking, I am visual, or has he passed me? Invariably I am the one who has to ask.
This happened yesterday. Conflicting traffic heading South, I heading North, he at 5k, me at 6k.
I heard him talking to the same service I was on, but neither he, nor the controller, was that interested if he was looking. Only me. I saw him as he passed underneath, I then told the controller I had been visual, but,,it was only me doing the talking, if you get my drift..
However, I was vigilant and on the plus side, knew he was there.
@ BeechBaby
"Conflicting" traffic heading South, I heading North, he at 5k, me at 6k
that means 1000ft vertical separation which is ok - not conflicting -the other one was on the same freq, so the controller knew he did not intend to climb through your level. If their workload is high, they don't give you a traffic advice in those cases.
I am "pleased" to report that my £12k TAS605 has possibly paid for itself today...
I think you need to expand on that post. Who tried to hit you?
2 or 3 factors combining into a loss of separation.
Very easily done, clearly.
