OK, got it working with "Excellent" signal and antenna vertical. Achieved by moving the router in the lounge 1m closer to the outside wall and raising the height by almost 1m.
The PC is still in the wrong place though, so it looks like an antenna extension lead, something like this, is called for:
click here so I can put it where it is most practical.
Says on the Linksys Box
"Put your desktop PC anywhere you want. High-speed networking without wires". Hmmm.
Have a nice weekend everyone :-)