There are quite a few threads on this board about the home hub 5 wireless speed, so it may be worth reading a few of them, and see if you can determine the cause.
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If your speeds when connected by Ethernet are Ok it would obviously indicate a wireless problem, most likely interference.
There are a few things to try and improve this.
Try a factory reset of the homehub by pressing a pin into the recess button on the rear for about 20 seconds. This often sorts out wireless problems.
Download a Wifi Analyser app for you smartphone if you have one or use the free version of inSSider from forum member Keith Beddoe's website here
It will show you the wireless channels and which one your Homehub is on. You want to find the channel with the least congestion, ie. least number of users. Once you have that you need to change your homehub onto that channel. This will turn off "smart wireless" whic is not as smart as BT think.
See link how to change channel on homehub
You should also check that the wireless network card drivers on your computers are up to date. Use the card manufacturers website rather than Windows which can be out of date.
Once you have done this try another speed best but don't reset the homehub again.