Can you try a different router?

haven't got another one here. Going to ask around and see if I can borrow one

Failing that try the tv in a different room switched on for testing purposes, the furthest away from the telephone socket incoming cable and router , see if it
1 stops causing issues confirm by checking (tbbqm )
2 or is less severe than it was before you moved it
If either of those observed then maybe having the tv in that room all the time or moving the bt master socket and router into that room, and running a Ethernet cable under the floor in to the room with tv in or just use wireless maybe are viable option's to you

get some tin foil and put it around a box. Put your router in it and connect the router to the test socket behind the master socket. Plug your pc directly into that. What happens then?

http://www.thinkbroadband.com/ping/share/55a0bc231cf...

you can clearly see the effect turning the tv on did there

does the tv also interfere with [am/mw] radio stations?

It doesn't appear to, no

Contract
Regarding your Plasma TV, legally you must first approach the SUPPLIER, not the Manufacturer, for a solution.

Legally, your Contract is with the Supplier - who may ask you to co-operate with the Manufacturer - but keep careful records of all correspondence and contacts.

You may also wish to notify and copy to Trading Standards.
If bought by Credit Card and more than £100 was involved on that Card, you should also notify the Credit Card Card company and keep it updated on progress or otherwise.


Testing
As well as the various Tests suggested by others, I would recommend-

1) With the TV OFF and Unplugged, Switch the Router OFF and note the results including any signal levels showing on your various devices

2) Switch the TV ON; and again note the signal levels showing on your various devices

3) Leaving the TV ON, Switch the Router ON; and note the signal levels

4) Switch OFF and Unplug the TV, keeping the Router ON, noting the signal levels etc.

During 3 & 4 you should also try making connection with at least some of the devices, at least one cabled directly to the Router and one using WiFi.

Additionally, you should try those tests with the TV in Standby Mode as well as fully ON. Most recent TVs have Switching Mode Power Supplies internally; and the problems may be arising there rather than in the Plasma Screen.

From experience of doing similar cross-checks on other devices, you may wish to make out a Test Plan, to ensure that you do not forget or confuse some of the steps.

Record the results on that Test Plan; and copy it to to the various parties.

I had the exact same issue, my Samsung plasma TV took out my ADSL2+ when it was turned on, CRC errors mounted up into the millions and noise margin dropped off massively.

No amount of tin foil or moving of the router fixed this, I had to sell the TV and get an LCD TV which doesn't affect the connection what so ever.

I think manufactures really don't give a [censored] what they make or how their products affect or services.

Just read this thread. It sounds like this might be common with Plasma tv's. I got a 50inch LG plasma and it causes my noise margin to drop by about 2 or 3 db. Altho it doesn't seem to affect my connection much. Unless i sync when the tv is on then il sync slower than normal. But if it syncs at its usual 8.2mbit or so with the tv off when the tv is on after that it doesn't make it disconnect or do anything bad.

Also and this is curious i never noticed my noise margin dropping or being affected at all by the plasma before i upgraded to adsl2 llu