I think I may have sorted it - a 'Parental Control' setting on the router had been switched on...which over-rode all DNS related changes I was making. I switched that off and...it works!!
One small hassle is that I appear to have to switch to a US based iTunes account in order to get the RP app to appear - will be if I can find a solution to this..
My broadband is with Spark. What's the advantage of a static IP?
Thanks for you help!