What does this say ?
Weight of Spitfire - about 2500kg
Weight of Harrier - about 5500kg
So KE of Harrier will be greater, unless Harrier is flying very slowly.
Flammability of A1 v Avgas not really an issue in the event of a crash - both will go up, for certain.
Full fuel load on a Harrier is about 3200kg, Spitfire 700kg (depending on model/mark)