Ethernet/Wireless speed issues

[#1]

I'm on the fibre to the cabinet connection with a Technicolor TG582n.
Connection to my PC via Ethernet cable is perfect, always getting 40mb download speeds, this is perfect whether something is connected via Wireless or not.
However, my wireless connection is very up and down. When the Ethernet connection is disconnected or the PC is turned off, my wireless speeds are equal to what I get via Ethernet.
The trouble comes when my PC is using Ethernet and I am trying to use the Wireless as my wireless speed totally drops off to speds lower than 3mb via SpeedTest.
I've seen a few threads complaining about this router but nothing yet about my problem, any help?

[#2]

Hi there,
I'm just wondering if the PC is doing anything to take up bandwidth from your connection when you connect that through Ethernet, for example is it downloading updates or anything else that might be connecting to the internet automatically?

[#3]

Nope nothing running, and when I do download something on my PC it is at 40mb or so.

[#4]

Is your PC running any P2P or file sharing software?  When it is doing nothing, it could be sharing files to other down-loaders.  I recall accidentally installing some file down-loading application and my ADSL service started to behave like a dog.  When I checked out the usage stats, I'd uploaded much more than I'd downloaded!!!  The blasted software was acting as a file redistribution service.
Such circumstances might exhibit the conditions you describe.  When the PC is switched off, your wireless devices see the full DS and US capacity.  When your PC is switched on, though apparently doing nothing it could be hammering the US capacity, thereby severely impacting the speed tests on the WiFi connected devices.
Do the WiFi connected devices indicate what the WiFi speed is?

[#5]

As I said, I've tried it without anything on the PC being used to download anything. No streaming/Steam/p2p clients etc.
When the PC is running I get download speeds less than 3mb/sec.
I've seen numerous other complains about this router, could it be that the router just isn't up to scratch?

[#6]

If you think it is the router, you could run the tests with a different router.  From the description you've given I think that there is something hickey with the PC if you can get better wifi download when you drop the PC off the network, then it is using some  BB bandwidth.

[#7]

I don't have another router, I recently moved into my flat and signed up for PlusNet after having great service from them at my mum's.
I've been playing around and have run a speed test on my tablet with the computer off and received a download speed of 0.68mbs. This was positioned less than a foot away from the router. When I turned the PC on, that achieved nearly 40mbs.
Judging by this review I have to ask why PlusNet are supplying a product which clearly isn't up to the job.

[#8]

You say that there is nothing running on the PC that would use up your bandwidth.  You could be certain of this by running task manager- resource monitor- processes from all users and look at the network traffic.  It would tell you if there is something running on the PC  that you don't know about.