By Mike Collett

LONDON (Reuters) - Tim Henman has warned that increasing betting in tennis could risk the integrity of the sport. Henman, 33, the former world number four, says in an interview with BBC television's Inside Sport program to be broadcast on Monday that he has heard of players being asked to influence the outcome of matches.

"I personally have never experienced it but, listening to the players talking, it seems it goes on," said Henman, who ended his 14-year career at the weekend by helping Britain to a 4-1 win over Croatia in the Davis Cup at Wimbledon.

"We've got to be very careful, very vigilant about it as tennis doesn't want to be associated with that."

Henman's comments come a month after the ATP began investigating possible irregular gambling patterns on a match at the Sopot Open in Poland between world number four Nikolay Davydenko and Martin Vassallo Arguello of Argentina.

Davydenko denies any involvement and will give his version of events to the ATP next month.

Etienne de Villiers, the chairman of the ATP, said in a statement: "All professional sport needs a level playing field in order to maintain its appeal and integrity.

"This is especially true for tennis which is a one on one gladiatorial contest. The ATP, and all involved with tennis, therefore treat any form of corruption extraordinarily seriously and we have established rigorous procedures and programs; and severe penalties for transgressing our codes of conduct.

"With regards to the recent match involving Nikolay Davydenko and Martin Vassallo Arguello, we have instigated a full ATP investigation and we will be using all means available to us - including independent, external resources - via our Anti-Corruption Rules to conduct a complete and thorough investigation."

"That said, it is important that we not jump to conclusions especially when players' reputations could be unfairly tainted.

"What we must do is carry out a comprehensive and immediate investigation and that is what we are doing."

SERIOUS ACCUSATIONS

Henman tells the BBC: "There have been some pretty serious accusations in the tennis world and I, for one, will be interested to see what comes out of it.

"No-one has ever approached me. I obviously wasn't the right material. People have always bet on tennis but the magnitude seems like it has increased.

"It's an easy target because it's a two-horse race and there is a lot going on. You talk about a Grand Slam -- there are 64 men's matches and 64 women's matches from the first round and there is a lot that can be bet on."

Henman also says there should be tough penalties for any player found to be involved in betting irregularities.

"We have to be sure from a player's point of view that anyone who is involved shouldn't be allowed back in the game for good," he says.

Roger Draper, chief executive of the Lawn Tennis Association says in the program he also believes that tennis has a problem with betting.

"I think we would be looking at the world through rose-tinted spectacles if we thought it didn't go on," he said. "I think the way it's going it's becoming as big an issue in sport as doping.

"I think most of the sports are hooked on to it. Sport is the second fastest growing sector of the economy at the moment - and the biggest growth area is betting.

"So we have to keep our eyes open, our ears to the ground and work with the betting companies rather than just ignore the problem and think it's going to go away. It isn't going to go away."