The extent of potential corruption in tennis is under scrutiny once more after a leading sports gambling watchdog stated that 73 matches suspected of suspicious betting activity were reported to the Tennis Integrity Unit in 2015 – more than three times the number of incidents involving any other sport.

Earlier this month, the Guardian revealed that two international tennis umpires were secretly banned and four others faced being thrown out of the sport for life on charges of serious corruption after allegedly taking bribes from betting syndicates in exchange for manipulating live scores on the International Tennis Federation’s Futures Tour.

That followed allegations during the Australian Open that 16 players who have been ranked in the top 50 had been repeatedly flagged to the TIU over suspicions they had thrown matches in the past decade. The ATP and WTA tours, the grand slam board and the sport’s governing body, the ITF, commissioned an independent review into their anti-corruption practices as a result.

However, new evidence released by Essa – which issues suspicious betting alerts to regulated bookmakers across Europe when irregular activity is spotted – in their quarterly integrity report on Thursday revealed 73 tennis matches had been flagged up to the authorities in 2015, with 24 occurring in the final three months of last year.

In comparison, football attracted 19 cases throughout the whole of 2015, with eight of those occurring between October and December, while three other sports – greyhound racing, snooker and ice hockey – had one case each in the final quarter.

“The start of 2016 has seen a worldwide focus on alleged match-fixing in tennis,” said the report. “The data contained in Essa’s Q1-3 reports has been used to highlight those concerns. The data in our Q4 integrity report reflects previous quarters, and whilst tennis constituted the largest proportion of suspicious betting alerts identified by Essa members, it should be noted the vast majority of tennis events are fair.

“That position is a reflection of the general trend shown in the previous three quarters of the year and therefore the overall position in 2015, which included a total of 100 cases of suspicious betting on sporting events, led by tennis with 73 cases and followed by football with 19,” it added.

In response, the TIU issued a statement that acknowledged it has been working closely with the watchdog. “If the analysis suggests suspicious activity, the TIU moves to investigation, which includes interviewing players, taking phones and laptops,” it said.

“An alert can be an indicator of suspicious activity. But it is not proof or evidence that corruption has taken place. On its own, betting data is not sufficient to bring forward a successful prosecution; it has to be considered, assessed and verified along with the TIU’s many other sources of intelligence. Statistics of the kind released today by Essa must be considered in that light.”

Geographically, 38 of the alerts originated in Europe, 24 in Asia, 16 in North America and 11 in South America. Africa accounted for nine. Most of the cases of suspicious betting in football occurred in European matches, which featured in 68% of cases in that sport. Tennis was more evenly spread globally, led by Asia (19 cases), Europe (18) and North America (14).

On Wednesday, the Thai doubles player Jatuporn Nalamphun was banned for 18 months for betting on unspecified matches then failing to cooperate with TIU investigators. That came after the United States Tennis Association admitted it was “shocked” at the Guardian’s revelation that banned umpire Denis Pitner was a line judge at both the US Open last August and also at an ATP world tour event in Doha last month which featured Novak Djokovic and Rafael Nadal.

The ATP blamed a “breach in procedures” for Pitner being allowed to work in Doha, with a spokesman confirming it would also review the issue to ensure it did not happen again.

The independent review, which commenced last month and will be undertaken by a three-person panel led by Adam Lewis QC, is expected to take at least a year to complete.