The Euro 2020 soccer final between England and Italy in July was a "superspreader" event due to the level of Covid-19 infection found in or around London's Wembley Stadium on the day, according to official data published on Friday.
Public Health England said 2,295 people were likely to have been infectious with a further 3,404 people potentially acquiring infection at the July 11 match.
"Euros final was superspreader event," declared the Times newspaper.
The match, with a crowd of around 67,000 inside the stadium, was England's first final in an international soccer tournament since the country hosted and won the 1966 World Cup.
"Euro 2020 was a unique occasion and it is unlikely we would see a similar impact on Covid-19 cases from future events," said Jenifer Smith, Public Health England's deputy medical director, in a statement.
"However, the data does show how easily the virus can spread when there is close contact and this should be a warning to us all as we try and return to a cautious normality once again."
Other trial events over a four-month period showed far fewer positive tests, and were either broadly in line with or lower than national averages.
The British Formula One Grand Prix at Silverstone in July drew a 350,000-strong crowd, the largest in Britain in more than 18 months, over three days and had 585 cases recorded by NHS Test and Trace.
Of those cases, 343 were likely to have already been infectious around the time of the event and the rest likely to have acquired an infection then.
The Wimbledon tennis championships, with around 300,000 people attending over the two weeks, recorded 881 cases.
"We've shown that we can reintroduce mass sports and cultural events safely but it is important that people remain cautious when mixing in very crowded settings," said Culture Minister Oliver Dowden.
"So that we can keep the football season, theatres and gigs safe with full crowds this winter, I urge sport, music and culture fans to get the vaccine as this is the safest way we can get big events firing on all cylinders once more."