<font face="Verdana, Arial, Helvetica, sans-serif" size="2">Originally posted by filberts sst:
Can it be seen from T3 or the walkthrough between T1/T3 ?</font>
If you really mean T3, then the answer's no.
Have a look at this map of LHR -
http://www.concordesst.com/graphics/lhrviewmap.jpg - I think that G-BOAB is next to runway 23 (the one that slopes from northeast to southwest) about east-northeast from the Europier between T1 and T2.
But as there's no formal walkthrough between T3 and T1 (other than underground), I'm not sure exactly where you mean.