Hold on, when you do a BT Speedtest check, does it say that the upload profile for your line is max 10Mpbs? If so, then it sounds like you are on the original Infinity(1). If so, you won't get what the original estimate says. Not sure when you actually took up infinity but it may have been before Infinity2 was rolled out. You may need to activate the 80/20 "for free" on the BT.COM website. However, if you do that, you will have to enter a new 18 month contract.
They say in the op that they are on the 40/10 package but the estimates did originally show their line was good for 72/20 but that figure changed to 35mbps download.
I was on the original 40/2 package, then upgraded to the 40/10 package when Infinity 2 was rolled out.
Yes my upload profile is at 10Mbps. If I use the BT line speed estimator - from the BT's website it used to say that with Infinity 2 I would get around 72Mbps down and 20Mbps up.
Now it states 32Mbps down and 20Mbps up!
I've just ran the BTW Performance Test. I have a download profile of 38.71Mbps down and 10Mbps up profile.
The achived speed is 37.51Mbps down and 7.96Mbps up. - Not bad for Wireless.
That is very strange that the download estimate is now 40mbit lower than before. I wonder what happened. It's also strange that the upload estimate remained the same at 20mbit. One would have expected upload to be affected by the same factors (line length, noise etc) as for the download. Maybe worth pushing back to get it investigated further?