Two points here.
Regardless of how tactfully the issue was raised, there
is an issue about the level of control exercised over VFR flights in class D, and the nature of the separation provided. The UK interpretation tends to err on the side of control and separation, while ATC in other states take a rather more minimalist by-the-ICAO-book view that you give the IFR flight traffic info and that's it. I'm not suggesting that one policy is better or worse than the other, but it's worth noting that there is a difference.
The commander correctly pointed out that the pilot of a VFR flight is responsible for separation provided traffic information is issued in good time and refered to the Air Naviagtion Order.
This is not correct, or at least not complete. The pilots of both aircraft are responsible for separation according to the normal rules of the air. For example, if the VFR flight is approaching from the IFR flight's right, it is the IFR flight's responsibility to give way. Which gets back fairly quickly to the "safe and expeditious flow of traffic..." thing
