HD films usually use a bit rate of higher than 3 Meg, more like 4 to 5 Meg. So basically your line is not up to the task of HD streaming, downloads and watch later should be fine.
On the upstream, as you are on what looks to be an ADSL only line, then with BT your only option is the 448Kbps upstream. Subscribing to another provider and paying more (to get a more business style connection) may get you 832 Kbps upload.
Alternatively see if TalkTalk or Sky have a LLU presence at your exchange. Downstream may not be much different, but upstream will more likely be in the 700 to 900 Kbps range. (twice the speed of now).
I am assuming you just mean you can't upload to youtube because of the time it takes, rather than it not working at all.