I was under the impression that was an English practice.
Indeed. Many British vehicles were positive-chassis right up until the 1960s.
This is rather interesting with all you US people saying that the Positive is always the Pole Grounded, here it would be the Negative,
Don't N.Z. telephone exchanges use positive ground on the batteries?
Of course our biggest source, traction power, has the negative return at a near ground potential.
As does the traction power for the 3rd-rail system employed on the southern region in Britain as well.
The London Underground (subway), however, actually uses a 4-rail system with neither pole solidly grounded. Balancing resistances are used to set the potentials in a 1/3 to 2/3 proportion, resulting in nominal voltages of about +420V and -210V relative to ground.
The outside conductor rail is the positive, central rail is the negative: