Thanks guys.
After a little searching around, my Belkin router would definitely appear to be the culprit. No multicast settings/features at all. 😕
Just out of interest, can anyone recommend any routers, or preferably modem/routers, which definitely do support multicasting between their wired and wireless networks? I bought the Belkin in haste a few weeks ago as a quick, cheap replacement for my dear-departed D-Link, so I’m sure I’d be able to returm it to the store and trade it in for another model.