Tried my wife's computer on ethernet and speeds are way uo to 14! Must be something to do with the wireless connection but why the difference in speed tests on here and on the bt test site?
1. Wireless is hopeless.
2. Speedtest sites are notoriously inaccurate (and easily overloaded).
The BT test is able to bypass general internet (and ISP) congestion, and test just your line back to the OR equipment. Every other speedtest site also reflects "issues" with the internet, ISP back-bones, etc.
Find a speedtest site and stick to it (and get comparisons between different tests on the same site).
The Flash based testers normally give high results (sometimes higher than the line speed).
The Java based ones seem to give more consistent results, but there are so few of them (I've only found two which are in the UK and, thus, able to give 74Mbps results for an 80Mbps line).
There is no better way [to test download speed] than actually downloading a file.
A single download thread (what you get when downloading through your browser) will normally give a lower speed than a multi thread download (using download manager software). The difference is the key to resolving your problem (if it is, indeed, your problem and not just ISP throttling or congestion).
vDSL2 FTTC Infinity with BT
DL Sync 80Mbps
UL Sync 20Mbps