ally tank

yo.. does any 1 know if it is legal to put an ally fuel tank in the boot of a striped out mk1?  

my m8 bought a mk2 escort and put 1 in there but he built a fire wall on the other side of it..

wana put 1 in my boot bu duno if it will b legal 2?

cheers

Why? the standard tank is lowdown and in the centre of the car, surely the best place for it.