It goes by lots of different names, eg Plastruct, but basically you buy A4(ish) sheets of it, it's ABS (So solvent welds with normal model glue) & comes in a variety of thicknesses. They also do "engineering sections" of the stuff, ie lenghts of round tube, rods, box, square bar, I-beams, channels etc etc. It custs easily with a sharp knife, & bends easily with only minor heating. Most model shops have it, some craft shops have it, but best place to find it is in shops specialising in model railway stuff.
Have a look for the resto I did on an Audi Quattro somewhere on here... I built up a new radio box lid out of the stuff. More recently, I did an MSC deck for a Thunder Dragon (2x Thunder Dragons, the good & the ugly). If you look at the Cheetah in my gallery, the spade, axe, rear cage & body side-bars are all hand made from the stuff too. Oh, & look at my Wild Willy resto, lots of chassis fixing & a wheel rim out of the stuff. Theres also a red custom van in my gallery which had extensive body mods done to it - it started life as a Kamtec escort van banger body!
As I said, post a pic of the type of Jag you're on about, & I'll keep my eyes open
