Laptop causing Xbox lag

[#1]

Hello
I've been having problems with my Xbox live connection for months now. I can play onlne fine but when someone else uses the laptop at the same time the connection drops to unusable. Now I thought it was due to watching Youtube etc on the laptop but after testing it out it appears simply opening Mozilla makes the connection drop on the xbox significantly. Surely opening a web page wouldnt have such a drastic effect on the Xbox?
I've:
Set the Nat setting to open
Closed any programs on the laptop that may be using bandwith
Connected the Xbox to the router with a cable
A few months ago we had some problems with our line disconnecting and plus net tried a to change a few things their end to make the line more stable. In the end it turned out to be a hardware fault my end but I was wondering if something they may have done is causing a problem?
Any advice would be appreciated.
Thanks
Ping: 55ms
Download Speed: 3.4 Mbps
Upload: 0.37 Mbps

[#2]

0800 587 1102, Xbox Live helpline, will probably be EXTREMELY busy today if they're even open.
And the support pages on www.xbox.com.

[#3]

I spoke with Microsoft and after running through all the checks they told me to contact my ISP. The connection is great until I start using my laptop, simply opening up my internet browser grdins everything to a holt. Could there be something running in the background on my laptop im not aware of draining all my bandwith?

[#4]

First thing to try
Install NetworX on the laptop and see if there is any usage http://www.softperfect.com/products/networx/
Second if nothing shows up  - try disabling the wireless on the laptop and connect wired

[#5]

You have a slow connection, with no extra buffer speed for anyone else to be online at the same time while gaming.  If running peer to peer games then that upload speed of yours is most likely why, as that will be getting capped out by your console alone, then someone else in your house hold goes online and they is none to spare so you get lag.
All it takes is opening web pages/checking email/twitter and the spiked load on your connection is simply higher than it's capable of for the time that the program is requesting the data from which ever site etc
You have similar connection speed to mine and all I can say is, gaming and anything else online do not mix.

[#6]

Profile on our side was stuck and set too high.  I've just fixed it. Disconnect and reconnect your router and give that a test.