Well, according to information on speedtest.net, for the UK in terms of bandwidth (both up, down and 'quality') I'd say sky actually pretty crap as an ISP, Virgin ironically is the best by far, with Plusnet in second, and BT in third.
The UK internet relies on the same copper cables that have always been used and they are enough, but the hardware used in the exchanges needs upgrading, and in many areas, especially more quiet or rural haven't had the exchanges upgraded. All you can do is put up with crap speeds and hope they might upgrade the exchange in your area some time in the next 5 years or move. No matter what ISP you choose, they will still be limited by the same network infrastructure, the only difference is if they rent it for more, they get priority usage or a 'bigger slice of the pie'.
But with the choice of ISP again. Sky has rubbish bandwidth overall and Virgin gives you crap network hardware and throttles/shapes like a beast. Now that leaves Plusnet and BT, it might surprise you to know Plusnet is owned by BT, they are the same company, Plusnet branded is though cheaper and has better results overall regarding bandwidth though their network hardware is cheaper than BT branded, some people have seen improvements when replacing filters etc.
I'd recommend you go with Plusnet, but see what BT offers you and compare the two, if they offer the same thing for the same price you may as well get the better BT branded network hardware.
Edited by Bearybear - 9/30/13 at 12:18pm