For the past few years I've lived in properties with only 1 Satellite signal into the property, making Sky+ functionality limited to one channel at a time - and not allowing you to schedule recordings without making sure you're on the right channel.
Unfortunately and what many people realise is that a satellite feed is actually a two way signal unlike a normal TV Aerial you can't just split it easily - if you did only certain channels would work together at the same time.
There are 4 possible settings for the signal, so channels are grouped into 4 groups. As long as you're watching something in the same group, both feeds work simultaneously. If not, you simply get the usual "No satellite feed" message. You can find a list of channel groupings HERE to know which channels are compatible with each other, but this list is out-of-date and some entries appear wrong.
Here's what I bought for under £10
2 Way Satellite / NTL / TV / BB Splitter SKY + F Plugs
Together with a couple of F Connector Satellite Cables I plugged the whole setup in, and it worked as described - it's not perfect but it's a lot better than no signal at all and all for less than a tenner!