Ok, thanks for the input everyone. It seems the general consensus is that the placard is not authoritative, so I shall, when I am sufficiently bored, investigate the ANO's requirements for night/IFR flight in detail to see whether my hypothetical situation is in fact real.
Chilli, I will try to have a chat with our engineers, but they are a sarcastic bunch and the chances of me getting a straight answer out of them are somewhere between zero and none!!!
Smurph, I don't know the details, but I know that IMC/IFR flight in helicoptors is very restricted. But since they seem to be able to fly VFR in just about any weather it very rarely seems to bother them in practice! Fortunately, for us guys with fixed wings who actually need to see where we're going because we fly too fast to read road-signs, the rules are less strict
FFF
--------------
[Edit for spelling!]