thanks all.... foil didn't work!
I could move the sat box upstairs as we have another pair of cables running up to a bedroom which we left in place when we moved to second box downstairs but the slingbox needs to be hard wired into the router which sits in the corner of the living room. Slingbox do another device which can be attached to the router and wirelessly transmit the signals to the slingbox but it is quite expensive and I didn't want to go down that route.
Seems that after I googled SkyEye to find out exactly what it does, I'm far from the only one with this problem with multiple Sky HD boxes.... ended up back at my usual technical (av) forum. Even moving the second box into the dining room next door or even upstairs may not cure the problem
I was hoping to sort this out without throwing even more money at this setup but Nick29, I think you have found a solution with the SkyEye gadget... only problem I have now is I'm 6000 miles away from the UK and I don't totally trust two 22 year olds who are not very technical to sort it out. I'm also not totally convinced this device will stop a remote control in the room from operating the 2nd box, or even allow the slingbox "virtual" remote to work
I'm very tempted to throw one box out the window, cut my subs down and leave the kids to freeview
thanks again for your input though