At the European Championship of 1976 in Yugoslavia, Thomas was the referee of the semi-final between Czechoslovakia and Holland. In the extra time of that match, he failed to notice a rough foul by Antonín Panenka on Johan Cruyff, after which Zdenek Nehoda was able to score the decisive goal.
Thomas drew the ire of Everton fans when, during a 1977 FA Cup semi-final against city rivals Liverpool
, he disallowed a late goal, also from Bryan Hamilton, which seemed legitimate and had gone largely uncontested by even the Liverpool supporters, and would have taken Everton to the cup final as 3-2 winners.
He also blew the final whistle seconds before Zico of Brazil scored what would have been the winning goal from a corner in a 1978 World Cup match against Sweden. He was also strongly opposed to extravagant goal celebrations, going so far as to break up celebrations and order players back to their positions for the re-start.
In the 1981 League Cup Final, Thomas allowed a goal from Liverpool defender Alan Kennedy
2 minutes from the end of extra time despite the fact that Sammy Lee, lying in an offside position, had to move his head to avoid being hit by the ball.