The a/c (??) was also featured on 'Tomorrows World' On BBC1 when it first went into service. It's the most advanced fire training system in the world (or was when it was first built). It also has a mock cabin interior (seats are metal to stop them melting) so the fire crews have a more realistic scenario when entering the a/c to find survivors/bodys, and also a staircase to the u/deck.
As other people have said, it is not made of any real a/c parts, but was built to represent the most common commercial widebody a/c fuselage/engine configurations, so it's a bit of everything.
The fire's are controlled from a small room/bunker nearby and also by remote control so the training officers can make any combination of possible a/c fire at the press of a button. Fire's are produced by a network of gas pipes running thru the structure.
Sometimes at LHR you might see the fire engines charging over to that direction (usually at quiet times of day) for a spot of regular training.
Also for those of you LHR regulars, did you know they had to dismantle it and repositon it, so that the VS hanger could be built ???.
"She Rolls, 45 knots, 90, 135, nose comes up to 20 degrees, she's airborne - She flies, Concorde Flies"