He is counted amongst the top 100 referees of all time in a list maintained by the International Federation of Football History and Statistics (IFFHS).
Very soon he showed his potential to be a leading referee and picked up a fair number of top division games.
When the original choice for the 1993-94 UEFA Champions League Final, Dutchman John Blankenstein, had to withdraw, Don took charge of the game in Athens, even though he had little over two years experience at that level.
He officiated in two matches in the 1994 World Cup: the quarter-final between Sweden and Romania in Palo Alto, and the first-round game between Saudi Arabia and Morocco in New Jersey.
This though led to tensions, particularly with David Elleray who preferred to maintain his teaching career at Harrow School rather than turn professional.