TAM never flew to London and at least as far as I know it never planned to do so. Varig currently flies GIG-GRU-LHR daily, continuing to CPH three times a week. Of course BA flies to Brazil as well. Daily LHR-GRU-GIG but this is to be changed to 4 weekly LHR-GRU-GIG and 3 weekly LHR-GRU-EZE.
You see, let me take a moment here to comment on something. Unlike carriers from all over the world LHR is not the main longhaul destination for Latin American carries, that "honour" goes to MIA. But even if we think about European operations alone, there are many airports airlines here would go first, before landing at London.
For most Latin airlines the main European target is, of course Madrid, (I don't think I'd have to explain why) and here in Brazil many destinations have more traffic than LON. I can think, in order of importance, of CDG, LIS, FRA, and MAD as having more traffic than London.
Hope it helps!