Thanks for all the replies guys I really appreciate it.
So just to update a little. I rang BT and they are going to send me out a new Smart 2 hub, with better wifi range. So in theory I should have a decent signal to the shed for wifi.
I currently have three PCs in the shed - two for meteors and one for imaging. All will need internet. I also have a switch with 8 ports (this came out of my work, when I needed a new one with 16 ports)
When the new Smart 2 hub arrives, I will then have a BT HUB 5 router at my disposal.
None of the PCs can pick up wifi as it stands.
@Carbon Brush im like you, networking I also see as sort of a black art!