The situation has been getting much more intersting as I took the 2wire device that had slowed down and did a factory reset, finding that in fact it does not fully reset it retains some information.
In the end, found that to truly to reset this it needed a complete reset using all the reset buttons found under diagnostics page used in order from top down, then a cold reset using the reset button from a switch off & on.
Then it allowed me to configure the dchp as I wanted and allowed me to set up the block to the provisioning server. Now the speed returned.
So now I started to test found on all the routers I had to test, The two 2wire units the Homehub 1.0; they all gave about 13+ Mps download which could vary to below 4Mps which is nothing like the promised 17+ from BT.
Then I found the information on setting the MTU & Rwin this now is getting much more interesting.
I tried to use Drtcp but found it a bit of a mystery but found TcpOptimiser and this came with a wealth of information on each adjustment so used this to tweak the settings for my Rwin. But MTU calculated as set.
With windows default of 65535 for Rwin the speeds were as before then tried 64240 again no difference in speed but then started to increase the Rwin by doubling the 64240 figure to 128488 and then the speed increased to the point where the tests seemed all to report 15+ Mps.

Now I ran your tests and the results are here .
http://s1201.photobucket.com/albums/bb346/grarcher/


Meanwhile I tried to talk to BT they said they would send me a new router as it would cure the problem they did but it was a Homehub2.0. It arrived damaged.
So now they are supposed to be sending me the Home Hub 3.0 which until I get this they seem not to want to help see why the speed is not as promised this magical 17+

But the question I ask is why must we have to study the system to this extent to get this speed and I live only 385 metres cable length from the exchange?

Lookig at those images, the two 2wires seem to get a nice consistent speed across the various sites with a quick rise, flattish top and quick fall. That is what I would expect.

The HH is a bit different ... the BT Beta and one TBB are rather rough! Was the failure caused by a HH issue?

In answer to your question ... MONEY! Everyone wants everything as cheap as possible, so BT and other ISPs have to cut everything back. At one time a technician would come and set up ADSL from scratch but there was a cost. How much extra would it cost to have another army of UK tech support and technicians going out and dealing with all of this? BT Business is more expensive, but support is UK based, response times to fault are NBD &c.

The failure looks to be a Java script error or an IE 8 error.
I keep getting a error log appear on my desktop for a java script error when accessing that site.
But one of the most annoying problems is IE8 keeps on having to recover the web page and it just will not allow the BT standard Speed test to run.
IE8 also has an annoying habit of freezing so you just have to close and restart. Its not a virus either as its well protected and daily updated. so far I have not found the cause its why I run chrome & Opera as I just cannot make up my mind on which one I like. I have to have IE8 for the main program I use it does not like the other two.