Well, as a Firefox user with a few "plugins", I was going demented when trying to get the banner working. Finally I remembered I use an "adblocker" in Firefox - I authorised the Tesco link and all was well ....
http://impgb.tradedoubler.com/imp?type(img)g(705131)a(1494391)
...
note it's the whole line above, even if your browser doesn't underline all of itThere do seem to be addons that will allow you the same functionality with IE7.
How you authorise the link will depend upon which adblocker tool you use - assuming that's the problem. There's a decent article here
http://www.tucows.com/article/1516 with screenshots to assist.
Of course, an adblocker may not be the problem. If you were just to paste the tradedoubler link (above) into the address bar in IE or Firefox, it should work regardless of adblockers and just display the banner - if it does, that's a pretty big pointer to a blocker.
If that doesn't fix it, I'm flumoxed!