It wasn't really allowed then, after it happened The FA banned it.Hated that donkey kick trick goal he scored with Willie Carr v us at Coventry. It was shown all the time on the tv sports shows when I was at school. It wouldnt be allowed now.
The 'reason' was; when Willie Carr put his heels either side of the ball to flick it up the FA, in their wisdom, stated; it is impossible for a player to simultaneously put 2 heels on the ball at the same time, thus he touched the ball twice while taking a free kick.