Difference between BT Broadband Speed Test and all...

Question

I have recently moved to BT Broadband from TalkTalk as I was dissatisfied with the speeds that I was getting with my TalkTalk line – they were OK outside of peak time but woeful in peak time.  With TalkTalk, I was on their ‘up to’  8Mbps which, in practice, translated to about 6Mbps for download outside peak times but dropped to below 1 Mbps in peak (around 500Kbps and sometimes even lower!) – these measurements were taken regularly with both the TalkTalk and Think Broadband speed tests which were usually roughly in agreement and I haven’t had to rely on memory as I downloaded the spreadsheet records available to Think Broadband registered users. 
I am now posting this in the hope that somebody can explain the difference between the BT Broadband Speed Checker (Here) and all the others available on the web.
When you are first connected to BT Broadband they warn you that your speeds will vary over the first ten days while they test your line to ascertain optimum speeds for it.  During that time, I checked it every day early, mid-day and evening (usually around 0630, 1230 & 2000 hrs) with Think Broadband and, yes, it did vary – the first day it started at around 1Mbps for download but rose to 10Mbps by the end of the day. On the second day, it rose to a peak of 17.8Mbps which was unbelievably fast to use (well, to me anyway) but never reached that speed again as over the rest of the ‘test period’, the download speed dropped and dropped to the point where I am now outside of the BT test period and consistently seeing only 2 to 2.5Mbps over a 24 hour period.
I emphasise that those speeds were all recorded using Think Broadband but I am now doing tests using the BT checker mentioned above and the speeds which BT indicate for downloads are consistently in the 14 to 18 Mbps range.  If I do the BT and TB test in quick succession, they generally show the BT calculated speed to be better than that of TB by a factor of around 7 (ie.  TB at 2 Mbps whilst BT show 14Mbps).  Now either they are measuring different things (or the sams things differently) or one of them is lying – all I know is that my general browsing experience is slower outside of peak times and I can tell by the time it takes to load pages. 
I might have misunderstood something in these tests but I am now beginning to regret that I fell I for the BT sales pitch which promised me ‘up to’ 20 Mbps but ‘more likely’ 17 Mbps.   I have tried to discuss thisl with BT Broadband technical support but they were no use whatsoever – indeed, I got the impression that he was reading from a script and as it didn’t cover my issue, I was wasting my time – it would also have helped for English to be his first language! 
According to the BT test, I am well within their ‘minimum guaranteed access speed’ (Here).  for my area (about 4Mbps) and therefore cannot do anything about it.  BUT that is only when measured using the BT speed tester – with any other, I am well below.  I am beginning to feel very conned and might even start looking to withdraw from BT if I cannot get this settled.
Can anybody help.  I will happily post detailed records of my various tests or router stats if they will help.
Thanks in advance.  

Answer 1

OK, I have now done all the tests etc. And here are the results:
ADSL Line Status from HomeHub 3
Connection Information
Line state:
Connected
Connection time:
0 days, 00:27:11
Downstream:
23.71 Mbps
Upstream:
1.176 Mbps
ADSL Settings
VPI/VCI:
0/38
Type:
PPPoA
Modulation:
G.992.5 Annex A
Latency type:
Fast
Noise margin (Down/Up):
3.4 dB / 6.4 dB
Line attenuation (Down/Up):
5.3 dB / 2.1 dB
Output power (Down/Up):
19.4 dBm / 11.6 dBm
FEC Events (Down/Up):
0 / 0
CRC Events (Down/Up):
41 / 24
Loss of Framing (Local/Remote):
0 / 0
Loss of Signal (Local/Remote):
0 / 0
Loss of Power (Local/Remote):
0 / 0
HEC Events (Down/Up):
20 / 7
Error Seconds (Local/Remote):
61 / 13
BT Speed Test Result
Download Speed:  6.59Mbps
Acceptable Range:  4Mbps - 21 Mbps
IP Profile:  21.42Mbps
Upload Speed:  0.99Mbps
Upstream IP Profile:  0.83 Mbps
Think Broadand Speed Test
Download Speed:  1.8 Mbps
Upload Speed:  0.9 Mbps
Uswitch Speed Test
Dowload Speed:  1.7 Mbps
Upload Speed:  0.9 Mbps
For what it's worth, I followed the guidelines for the BT test and took all of the tests within a 10 minute period.
All I know is that my daytime BT connection is nowhere near as fast as I had from TalkTalk.  Indeed, it was not even quick enough to watch non-HD YouTube videos earlier this morning without freezing to buffer.