At least 20 fans were injured, eight of them requiring hospital treatment. But there was confusion last night about what caused their wounds.
The British Embassy in Lisbon confirmed that rubber bullets were fired by the police. But Delfim Passos, head of police in Oporto denied this. He said although CS gas had been used "I can guarantee that not a single shot was fired. We evacuated the fans with more civility than I think they expected, and that was nice at the end."
But United fans, who were returning to Manchester when the trouble erupted, accused the police of carrying out un- provoked baton charges outside the ground before the match, and firing on people leaving after the match.
The Foreign Office said: "We are concerned at reports of injuries to around 20 fans ... We are aware of reports, and have also been told by a number of fans, that their injuries were caused by police batons and rubber pellets. We are seeking a full police report from the Portuguese authorities."
However, Portuguese police accused United fans of being drunk and violent. One senior officer said police "were forced to use anti-riot equipment".