I'm not sure if it would work. Experience says no. Reading some of the reviews on those 2 products it seems that only one device can be active on the ethernet line at once. Both devices can't be On together. I'm thinking its something to do with ip allocation, as the router would probably only see 1 device.. even though there is 2.
Something like that would be ok if you had a games console and a dvd player that you wanted both to be connected to the router. Though in that case you'd have to always turn one of the devices off in order for the other to work.
I think the solution is to buy a bigger belkin surge protector plug... or I'm not sure if this would still work, but maybe a dual plug adaptar. One that can plug 2 plugs in to one socket. They are probably cheaper than buying a big belkin protector.
Something like this http://www.amazon.co.uk/EAGLE-Block-Socket-Splitter-...
(btw, I'm not endorsing that particular plug. Just using it as an example so you know what I'm talking about).
Demon => Freeserve => Pipex => Be => Sky => BT Infinity 2