Ongoing problems with connection speed

[#1]

From previous experience with BT, and initially with Plusnet, my line can support a connection speed of 5-6 Mb.
However, I've been getting regular dips in service quality for several weeks now. On a good day we are getting 0.5 Mb/sec which I don't really think is good enough. Have tried alternative router etc.
From the BT wholesale tests, the IP profile is 0.51 Mbps.
Any advice on this would be greatly appreciated.

[#2]

Hello there. Are these speed tests over a wired connection? If so, I would recommend troubleshooting the fault at http://faults.plus.net and then potentially raise it, so that our faults team can investigate further. if the issue lies with the wireless connectivity, here's a guide to improving the wireless speeds.
http://www.plus.net/support/broadband/wireless_broadband/wireless_signal.shtml
Hope this helps

[#3]

thanks for the reply.
I've had problems with both wired and wireless connections. I've gone through the troubleshooting guide and will wait to see if this resolves the problem.