"Does anyone know if it was, or maybe still is, legal?"
As far as cremation is concerned, legal or not, it was frowned on by the church and is still mistrusted by many traditional Catholics
As far as I know, it was never a practice carried out by Irish Travellers.
The ones we spoke to knew of it happening among other travelling nationalities but looked on it somewhat askance.
Can't speak for Britain, but here in rural Ireland, nowadays it's virtually impossible to burn anything in the open air without a letter from the Pope (so to speak), air pollution laws being what they have become.
Jim Carroll