Business packages are 832Kbit upstream from most ISPs on "up to 8M" ADSL, so I'd be surprised if the BT ones aren't.
If your exchange has 21CN then you'll be on their "up to 20Mbit" range which claims "up to 1Mbit upstream" - I'm not sure if that is an enforced cap or a deliberately low estimate (LLU providers offering ADSL2+ usual claim "up to 1.4Mbit upstream").
If fast upstream is what you need, an FTTC provider may be a better bet if FTTC is available in your area - ~2mbit upstream in most cases if you buy a basic product, up to 10M if you are close to your cab and pay for a slightly more expensive one.
I was, I believe called Max Premium and it was over and above the standard service. You need to get a BT sales agaent that really know the product set.
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