It did raise a question though, what happened to the viewing area at the then terminal 2 (was it pulled down) ?
Actually it's mostly still there, albeit inaccessible to Joe Public now. If one walks from T1 to T2 through the Queen's Building, you do pass the Charles Blair P51 memorial which is in a still-recognisable part of the viewing area, which included a (now drained) pool, visible in the old footage.
The old viewing area would be less than impressive for spotting now that the terminals have been extended way beyond their original curtilages. Doubtless all will soon be swept away as part of the Heathrow East development.