(CNN) -- Brad Drewett is reluctant to divulge exact numbers, but the ATP World Tour Finals is a big deal for men's tennis.





The season-ending event, worth $5 million in prize money this year, is the tour's marquee event -- an elite eight-man showpiece that attracts top sponsors and acts as a massive advert for the game.





"It's one the of the ATP's biggest assets," longtime tournament director Brad Drewett told CNN during this week's round-robin matches. "For it to be a commercial success is extremely important for us."





Drewett, a 58-year-old former tennis prodigy, has been running the finals for more than a decade now.





It came to London's glitzy O2 Arena -- best known as a concert venue -- in 2009 after Drewett took it back to Shanghai for three years.





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"The actual financial structure is a bit different. We have a partnership here with AEG, the owners of the O2, whereas in Shanghai we had a partnership with the municipal government who were very keen to have the event for the purpose of promoting China and Shanghai and also promoting the sport of tennis in China," he said.





"Here it was us wanting to bring the event back to the traditional market of Europe, and in particular London."





The UK capital has a contract until 2013, but doubts have been raised about the event's future on the banks of the River Thames due to complaints about British laws which require players to be taxed on all endorsements during the time they are in the country.





The Lawn Tennis Association, which runs Wimbledon and is also an event partner of the ATP finals, is lobbying the government for an exemption.





"If we lose events like this it will have a big impact not just on the economy but also on sponsors and television and in other areas," LTA chief executive Roger Draper told the UK Press Association.





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Drewett said the ATP is happy for the event to stay in London, which is one of the ruling body's global headquarters alongside Florida, Sydney and Monte Carlo.





"That decision won't be made until the second or third quarter of next year. That's a decision for our board. We're very happy here," he said.





"We have every reason to believe that next year and the following year will be just as popular."





More than 250,000 people attended the 17,500-capacity arena over eight days in the first two years, and sponsorship has "sold out" with title partner Barclays bank joined by luxury-goods brands such as Rolex, Lacoste and Moet & Chandon along with the likes of FedEx, South African Airways, Nissan, Ricoh and Italian power giant Enel.





It is broadcast in the UK by public and subscription channels, and in more than 150 countries around the world.





"It's our marquee event and it generates a significant amount of money for us," Drewett said. "And from a promotional point of view this week is the event that everyone is talking about."





The 2009 rebranding from the Masters Cup has also given the tournament a distinct identity from the four grand slam events of the tennis calendar.





"A grand slam has two or three major courts, men and women, plus the outside courts over 14 days. To have quarter of a million in that time frame on one court is testament to the strength of the event and the players we have right now and their popularity," Drewett said.





"I personally like the rebranding. It tells a good story, it's pretty clear what it is. The message is very clear to the consumer.





"We're not looking to compete in any way with the grand slams. This event is what it is -- the format being eight players, only men, indoors, round-robin -- it speaks for itself as being totally different from a grand slam. The public understand that."





Drewett was one
How many people How many days does the event take place? what has happend to the sponsorship what is the marquee event of men's tennis called how many people attend the season ending tournament What is the marquee event What has sold out How many people attend? When will the decision be made?
250,000 eight "sold out" ATP World Tour Finals 250,000 an elite eight-man showpiece sponsorship More than 250,000 the second or third quarter of next year.
question: How many people, answer: 250,000 | question: How many days does the event take place?, answer: eight | question: what has happend to the sponsorship, answer: "sold out" | question: what is the marquee event of men's tennis called, answer: ATP World Tour Finals | question: how many people attend the season ending tournament, answer: 250,000 | question: What is the marquee event, answer: an elite eight-man showpiece | question: What has sold out, answer: sponsorship | question: How many people attend?, answer: More than 250,000 | question: When will the decision be made?, answer: the second or third quarter of next year.