I don't know if it's still applicable, but my old manager had a Triumph TR3 as a company car, apparenly it was all good things for the company as there are tax reliefs for old cars

but they have to be fairly old, so you are looking at an original Mk1 probably
Also the resale on an older car is better, for example I don't really see me loosing too much on my Mk2 and Mk1 prices are going up (and rightly so, they are lovely

)