Fans gather outside Twickenham Stadium in London before a game Sunday between the New York Giants and Los Angeles Rams. The NFL has had its eye on the city since the 1990s. (Paul Childs/Reuters)

Joe Vincent grew up an entire ocean, and an entire culture, away from his true sports love.

In Britain, a place that reveres soccer as a secular religion, Vincent worshipped at the altar of a breakaway faith: American football.

“I’ve got my rugby and soccer teams,” said the 34-year-old police officer, whose native Wales is chock-full of both with nary a shoulder-pad-clad crew in sight. “I just happen to think American football is the most exciting sport there is.”

Until recently, that would have been heresy, punishable by long nights of (mostly) good-natured shaming at the nearest pub.

But no more. Football has taken root here, so much so that the idea of a London-based franchise — long dangled by the NFL, long deemed a fantasy — is looking more realistic than ever.

Bryan Walters runs onto the field before an NFL International Series game between Jacksonville and Indianapolis on Oct. 2. Walters’s Jaguars have become London’s unofficial “home” team. (Ben Hoskins/Getty Images)

When the Redskins take the field at 80,000-plus-seat Wembley Stadium on Sunday to square off against the Cincinnati Bengals, it will mark the third and final game played in London this season, all of them sell-outs. After 10 years of staging regular season showdowns in this city of 9 million people, NFL officials feel confident that they have built a large enough support base here to make a franchise viable.

“London would be up there with some major U.S. cities in terms of the number of NFL fans,” said Mark Waller, the league’s executive vice president of international.

And not just any fans: London, with its vast wealth, offers the NFL a potentially lucrative new market along with the sort of growth potential that the league badly needs at a time of sagging television ratings and a seemingly maxed-out fan base in the United States.

The NFL has plenty to offer in return: entry into the world’s richest sports league and a share of a powerful American brand. London’s mayor, Sadiq Khan, has become a prominent backer since taking office in May, with a spokesman saying that the city has proved it “not only has the best venues to host American Football, but the fan base to make a franchise a real success.”

Making its presence felt

Despite the desires of the city and the league to base a team here, significant obstacles remain, the most intractable of which appears to be basic geography.

A London-based franchise would be 5,500 miles and an 11-hour flight from the newly relocated Rams in Los Angeles. London’s closest opponent, the colonial rabble of New England, would be nearly eight hours away, putting the London team at a potentially substantial disadvantage as its jet-lagged players attempt to suit up against better-rested rivals.

“I think the big remaining issue is how do you know and how do you prove that a team could be competitive,” Waller said. “I don’t know how you test for it. The Seahawks are probably the most-traveled team currently, and they obviously can be competitive. It’s probably the only question that we need to answer.”

Teams that play games in London now are generally given weeks off afterward. But this season, the Indianapolis Colts played a home game one week after playing in London — and won.

Even so, a London-based team probably would have to have its schedule divided into segments, Waller said, so that it would spend several weeks at a time in the United States and then several weeks in the U.K.

The fact that the league is even considering such details reflects how far it has come on some of the larger barriers to basing a team in London. Perhaps the most fundamental: Would Brits ever regard American football as anything more than a peculiar bastardization of their beautiful game?

When London first started hosting NFL matchups, in 2007, the answer wasn’t clear.

Vincent, the lifelong NFL fan, said he remembers going to a game at Wembley that year and meeting other British “football geeks” who knew the sport, but also those who wouldn’t have known a cornerback from a quarterback.

These days, he said, “there’s a solid majority who fully understand the rules and get irritated when the obligatory wave gets started in the fourth quarter.”

Beyond the stands, American football has been getting far more air time. Some NFL games televised in the U.K. are carried by the BBC; most are carried on the Sky Sports network. According to Waller, viewership for NFL games on Sky is about 30 to 40 percent of the viewership of a Premier League soccer game.

Getting Brits to love, or at least notice, that other game called football has been a long process. The Jacksonville Jaguars, who play here once a year and have become the city’s unofficial home team, have spearheaded the effort.

The team has helped educate Brits about the sport, sending over players and coaches to teach young athletes at U.K.-based football academies. It has also set up a local fan club — the Union Jax — and helped to establish a modified version of touch football — JagTag — in dozens of British schools.

The relationship has “stabilized” the Jaguars’ once-shaky finances, according to team president Mark Lamping. “It’s just one game. But it represents 15 percent of our local revenue,” he said. It also has led to speculation that the team could be a prime target for relocation. When asked about the possibility, Lamping demurred.

“We’re focused on one game a year in London through 2020,” he said. “This is working really well for us.”

A faraway franchise?

But beyond 2020, the Jaguars, or another team, could be preparing to call London home. When the league began play in the city, officials said they envisioned a 15-year process ending with a London-based team. Waller has said he believes 2022 is a realistic target.

“Our job is to be able to say to the owners, ‘If you want to put a team here, we’re ready,’ ” he said in a phone interview. “I liken it to L.A. It took decades. And then a few teams decided they were interested, and it happened very quickly.”

Experts question, however, whether it will ever happen for London.

Matthew L. McDowell, who teaches sports management at the University of Edinburgh, said that the NFL has gazed longingly across the Atlantic for decades. For 15 seasons, after all, it ran NFL Europe, a developmental league.

But it has always stopped short of basing a team in Europe, and McDowell said he expects that will continue.

“The NFL knows they don’t need to do it,” he said, citing the boost the league already gets from staging several games a year in London. “They wouldn’t gain anything from it.”

Any prospective decision about placing a franchise in London would rest with the owners of the 32 teams. At least 24 of them would have to ratify any proposed relocation or expansion decision.

At the moment, owners have more pressing franchise-location issues to ponder.

The Rams moved from St. Louis to Los Angeles for this season. The San Diego Chargers have an option to join the Rams there; they could remain in San Diego if public financing for a new stadium there is approved. The Oakland Raiders might apply to relocate to Las Vegas, where public funding for a stadium recently was approved. The Raiders also would inherit the option to join the Rams in Los Angeles if the Chargers pass.

“I don’t think that’s on the radar right now,” one owner said of the possibility of a London-based franchise. “There would be a lot of issues with travel and whether it would even work. I don’t think there’s a ton of sentiment for that [among ownership] at this point.”

Nor, surprisingly enough, is there sentiment for it even among some of Britain’s most die-hard fans.

Vincent, for one, is cool to the idea of an NFL team moving to the U.K. He certainly doesn’t want it to happen to the Jaguars, who were his team of choice long before they had any relationship with London.

“I support the Jacksonville Jaguars,” said Vincent, who owns at least 10 of the team’s jerseys. “I wouldn’t want to see them become the London Jaguars.”

As much as the NFL may be catching on in Britain, he said he worries that with time “the novelty would wear off” and fans would lose interest. Besides, some cultural divides are simply unbridgeable.

“It’s America’s game,” Vincent said. “We should leave it at that.”

Maske reported from Washington. Karla Adam in London contributed to this report.