The study by accountancy firm Deloitte, commissioned by the NFL and a London marketing agency, also casts doubt on the feasibility of a Super Bowl in the British capital and warns of a negative reaction from the United States.
The prospect of a team being permanently based in London has been growing since the NFL first brought regular-season games to the city in 2007. With three games at Wembley Stadium this season, the British government recently offered its backing to persuade a franchise to base itself overseas.
The feasibility study forecasts the city enjoying an annual economic boost of 102 million pounds ($165 million) from hosting eight home games, largely driven by fan spending.
Including spending outside of the capital linked directly or indirectly to a franchise, Deloitte says a London team's total potential gross output in Britain is estimated to be 158 million pounds ($255 million) per season. Deloitte is assuming players and staff would play two games on four visits each season, rather than being based in London.
The report will be discussed at the next owners' meeting in 2015, said Mark Waller, the NFL's executive vice-president of international who is hoping the obstacles to a London franchise can be overcome.
"There is no value to anybody putting a team here and finding the rigours of the season do not allow it to compete at the highest level," Waller said. "So that's the work we are going to do. That's probably a five-year piece of work."
While the 30-page report paints a positive picture, there are reservations about Wembley hosting the Super Bowl.
A major hurdle to overcome with a Super Bowl in London would be selecting a suitable the kick-off time. Starting at 4 p.m. EST would be 9 p.m. in London and make transport away from Wembley challenging on a Sunday night. Deloitte says a 6 p.m. local time kickoff "may be unlikely to attract the desired television audience in the U.S.," where it would be 10 a.m. on the West Coast.
Predicting that fewer die-hard fans and season-ticket holders would be able to cross the Atlantic, Deloitte cautions that the atmosphere inside the stadium and on television could be affected and impact on the "wider global brand presence."
"The reaction from the NFL's core U.S. market could focus on the negative implications of moving a definitively 'American' event overseas for reasons that may be perceived as solely financial or commercial," the Deloitte report says.
If the NFL instead opted for expanding the International Series to four games in London, the city would still enjoy an annual financial boost of 58 million pounds ($94 million), Deloitte predicts.
The firm estimated that the two games in 2013 directly generated 32 million pounds ($52 million) for London, with league spending accounting for a quarter of that. Renting and securing Wembley cost 2.1 million pounds ($3.4 million) for the two matches.
The Wembley contract runs until 2016, but the NFL has not talked to West Ham about potentially using the revamped Olympic Stadium in east London.
"When we looked at that venue before West Ham took it on it wasn't clear to us how it was going to end up as a venue," Waller said.
Sajid Javid, the British cabinet minister with responsibility for sports, said the appetite for the NFL is growing and the report shows the "cynics are wrong."
"The NFL has a huge fan base here," the culture secretary said. "I hope it will become a second home for American football."
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