Hi,
If you have the correct software on your BeoVision 3 it should not be too difficult. I think you may have it set up incorrectly tho. Go to Connections in the BV3 menu, select which ever AV scart you have the Sky + connected to press GO, then scroll through the options to find DTV/SAT and then press GO, your Set top box controller list should appear, scroll down to Pace sky + (or if Thompson Sky+ is listed then select that one instead), then press Go to store that. It will then ask you when you want the sky box to switch off, for it to Follow TV or Never switch off etc, choose which one you desire.
Once all this has been stored, it should be plain sailing, but check the IR cable is plugged in to the TV and that the IR sensor is placed correctly on the sky+ box (may need to play around with the placement).
I hope this helps.
Vinnie.