No-one's doing any hammering but if you're a commercial pilot who's used to flying in controlled airspace clearly the key heads-up for you is when a controller says "leaving controlled airspace, radar advisory service" or worse. I'm sure that's a cue to you and your pal on the flight deck (if you have one) to start communicating about who's doing the lookout and who's got their head down in the cockpit.
But there are more insidious scenarios. The worst in my view is when you go from Class D to Class E. There isn't much Class E in the UK (Scottish and Belfast TMAs only) but a controller won't alert you when you make the transition because it's all still controlled airspace. You're still on a radar control service which makes you feel all warm and cosy but what you may not realise is that Jimmy in his microlight is out there flying prefectly legally VFR in the same chunk of airspace without speaking to anyone.
NS