OK having read the suggested articles when I posted this (that didn't show up on an initial forum search...) I believe the hidden SSID is the network used by the nodes to communicate with each other, and so isn't the cause of the interference, which I assume now is the Sky network on ch36. But my last question remains, is it possible to change the channel used by the Decos? I know out of the box it was on ch36 (the same as the Sky network, that was fun...) and it's been on ch48 previously, and now on ch44, but I don't know what triggers the change. Is it when all nodes are restarted, does it look for the best channel available?

Update on this - have turned off all the Sky equipment now so only the Deco kit is on and broadcasting - however the Deco app is still complaining about significant interference, which as far as I can tell is only the Deco broadcast and hidden private networks - is this correct?