I remember Peter Coyne getting a hat trick for England Schoolboys v West Germany in 1974. I remember it as it was live on TV and it was such a big deal to have any kind of live football in those days. Apart from that it was the Cup Final and a few (not all) England games. Hard to imagine now..
Recalling this makes me feel very old!
Coyne actually scored 2 hattricks for England Schoolboys while at United.