Up to 30,000 people were expected to converge on London's Hyde Park for the capital's biggest screening of a match since the European Championship in 1996, with other big crowds expected in Leeds, Manchester, Bristol and on Brighton beach on the south coast.
"They're already heroes, its just about whether they turn into legends," said 32-year-old Dan Woodbury as he waited for the 1800 GMT kick-off in The George pub at London Bridge.
Peter Cook, 33, had arrived to watch seven hours ahead of the start, leaving work on hold for the day.
"I'm not normally a massive football fan, but it brings everybody together," he said. "That's why I'm here - I don't want to miss that."
Daniel Ries, in his late 20s, was in no doubt of the match's importance: "It's the biggest game of our generation," he told Reuters. "I’m feeling excited. Really happy about today’s game."
The game is England's first World Cup semi-final since the penalty shoot-out heartbreak against the then West Germany in 1990 in Italy.
Roads and rail services were expected to be full from mid-afternoon as people left work early for the kick-off. The AA motoring organization predicted that by the time the game started, roads would be quieter than on Christmas Day.
The British Beer and Pub Association forecast that the number of pints bought would soar by 10 million during the game, many probably destined to be thrown in the air by delirious fans as in previous games - if England score.
But police warned against any repeat of the disorder that followed Saturday's win over Sweden, in which some revelers jumped on vehicles, including buses and an ambulance, and damaged shops.
After that game, police recorded 387 incidents and made more than 70 arrests nationwide.
"This is in stark contrast to the fans out in Russia, whose behavior, apart from a couple of minor incidents, has been great," said Mark Roberts, the National Police Chiefs’ Council Lead for Football Policing.
Politicians and royalty issued their own rallying cries.
"The whole country is right behind you tonight. Come on England - it's coming home!" Prince William, president of England’s Football Association, said in a statement.
Prime Minister Theresa May said: "Gareth Southgate and the boys have done a fantastic job and I'm sure that they're going to go on to do well and I wish them all the very best of luck tonight."
The winners of Wednesday's game will face France in the final at 1500 GMT on Sunday.
(Reporting by Jo Heywood and Isabel Woodford; writing by Stephen Addison; editing by Michael Holden)