Note that almost all speed checker results we have seen in the past have been underestimates, but BT put in place an updated speed-checker last weekend.
The reason for the change (in the checker) was to make allowance for the updates (in the cabinets) that now allow higher speeds (up to 80/20) for those closer to the cabinet - but those same updates also improve download speeds for those further away too (ie better download speeds up to 40/10), though they can also decrease the upload speeds.
The problem is that we haven't got much of a feel (yet) for whether the new estimates are still an under-estimate, or if they have made them a bit more accurate.
My current FTTC line was originally predicted as 29/11 and achieved 40/10. It is now predicted as being 40/18. I think many more people are getting predictions of 40Mbps.