Those D-Link hubs may be your problem. When I started it bought several D-Limks, was never happy with them. Sold them and replaced them with Rosewill 500's, no more usb trouble. I understand you can't get Rosewill in the UK, maybe ship from USA.
Possibly. I don't think it's worth shipping a USB hub from the US just to host 5GH of USB miners.
To be fair, I think I'm going to abandon the USB miners, they're more trouble than they're worth.