Hong Kong has bid to host the 2018 Rugby World Cup Sevens in a move described as an "insurance policy" by leading official Trevor Gregory. The Hong Kong Rugby Football Union had previously stated it would not bid for the 2018 edition as it could not host two major sevens tournaments - the Hong Kong Sevens and the World Cup - in one year at the Hong Kong Stadium. "But we have now put our hand up because we are not sure if the International Rugby Board will include Hong Kong as part of the World Series when they announce the cities in the next cycle. So as an insurance policy we have bid for the World Cup," said Gregory, HKRFU chairman. Of course, we expect to be part of the World Series in the future. But until the process is complete nothing can be guaranteed HKRFU chairman Trevor Gregory The IRB has confirmed an unprecedented level of interest in hosting elite international sevens events, underscoring the enormous global appeal of the newest Olympic sport. Twenty-five unions formally confirmed their interest in hosting a round of the popular HSBC Sevens World Series from the 2015-16 season. Twelve of the unions are also interested in hosting the showcase men's and women's World Cup Sevens in 2018. "Of course, we expect to be part of the World Series in the future. But until the process is complete nothing can be guaranteed and if for some inexplicable reason we don't get it, we would then hope we will be given the 2018 World Cup Sevens," Gregory said. Hong Kong has hosted the World Cup Sevens twice - in 1997 and 2005. The last World Cup was held in Moscow last June, but the IRB has now moved the next one back a year so it falls between Olympic years. Singapore is among the 12 unions that have expressed an interest to tender for 2018 along with England, Fiji, Hong Kong, Netherlands, New Zealand, Portugal, Scotland, South Africa, Spain, the US and Wales. The 12 have also expressed an interest to be part of the World Series in 2015-16. IRB chairman Bernard Lapasset said: "This unprecedented response truly reflects the enormous prestige and appeal of rugby sevens in the global sporting market place ahead of our Rio 2016 Olympic Games debut." Hong Kong is also keen that it becomes the last leg of the World Series with its tournament deciding both the relegation and promotion. Gregory said if the new Kai Tak stadium could be ready by 2018, Hong Kong would have a better chance of hosting both the World Cup as well as continuing to be part of the World Series. "It is not practical to do both at the old stadium. "And remember that hosting future World Cups means you host both the men's and women's event," Gregory said. "If we could be certain the new Kai Tak venue would be ready by 2018, our application to host the World Cup would be stronger."