Lets see:
Downstream: 18383 Kbps
Upstream: 1023 Kbps
My, how the other half lives

My paltry 2Mb connection is the limit of the copper between my flat and the exchange (which I am about as far away from as you can get before you are closer to a different one).
I would have thought that if your not using it for a download then surely that speed/bandwith could be used for uploading instead...
You are thinking of your connection as a data path to the intertubes that only you are using. That's not how packet switching networks operate. As soon as your traffic hits the network, it's threaded into a vast multiplexed stream of other data zipping back and forth for other users too. Basically, whenever you aren't using your ISP's bandwidth to receive data, it's being given out to someone else that is. Most UK ISPs try to cram as many customers as they can on their main pipes, since they pay a lot for them and only bulk traffic makes a profit. They aren't going to hold onto precious bandwidth for you to upload data unless you pay a premium for it.