OK, found some of the answers over in the Sky forum.
Thread here, very informative
Outputting Sky HD to 2 TVs
1. Sky-HD box does indeed output simultaneously on all outputs
2. As my bedroom LCD is HD-Ready, I would be mad settling for less than component or HDMI
Options are :-
1. Buy a pair of component baluns and a pair of stereo baluns, Sky-HD out via component and stereo, via 2 Cat5, into bedroom TV via component and stereo. Quite expensive, lots of cables
2. Buy a pair of HDMI baluns. This in my case will require HDMI splitters/switchboxes, on both sides as HDMI already used on both Sky-HD and LCD in bedroom
3. Buy shielded CAT5 cable, and solder phono plugs, x3 to ethernet, x2 to ethernet, giving a cheap solution. However, I haven't got a clue how to achieve this, I just wish I could get the cables made up.
That about covers it, ebay is the best source for cheap baluns, but not many around at the moment.