I've been having wifi issues, from back with Sky and also now I have BT Infinity too. Turns out it's my phone constantly dropping the wifi connection after Googling. However I did try changing stuff on my HH5 though. I assume you are using the same?
First of all, turn the power off to the router, give it 10 seconds then turn it back on again, let it reboot and get the blue light, then try your devices again. This fixed a recent speed issue I was having that a soft reboot didn't.
Next download an app called WifiAnalyzer, to make sure the channel you are on hasn't got too many of your neighbours trying to use that as well. Try moving to a clear channel and reboot the router. That's for the 2.4Ghz wifi btw.
If that has no success then try switching off the 2.4Ghz wifi and just using the 5Ghz. Assuming your devices support it that is - you can check if they use 5Ghz in the Wireless Devices part of the Home Network section in Advanced Settings. You could even give the 2.4 and 5 wireless different SSID names. You can sometimes get a better connection if your device isn't switching between the two if they have the same SSID.
Also in the same Wireless Devices section, click on each one and assign them a static IP address on your network, then click Always Use This IP. BT's hub uses 192.168.1.254 as it's gateway IP so give your devices their own number, i.e. Phone 255, Laptop 256, and so on.
You could also try checking the router logs to see if it's dropping the connection a lot. That would indicate a problem or a bad line. You can also do a "quiet line test" from your landline. Dial 17070 choose option 2 and listen to the line for any static or crackling/noises.
Lastly login and try the online BT Performance Test -
http://speedtest.btwholesale.com/ - Do the speedtest then it'll give you other options for more diagnostics.
Failing all that, fuck knows! You could try a different router instead.
