Rebecca Adlington may be the golden girl of British swimming but the double Beijing gold medallist has insisted she is "so worried it's unbelievable" ahead of the UK trials for the London Olympics. Britain's leading swimmers will look to book their spots for the Games at the trials, which will also double as a 2012 test event, which get underway at the Olympic Aquatic centre this weekend. To make sure of a place in 'Team GB', British swimmers need to finish in the top two of their event and also make the 'A' standard time set by British Swimming chiefs. Few anticipate that being much of an issue for Adlington, who became a national sporting heroine when winning the Olympic 400 and 800 metres freestyle titles in China four years ago. "I'm so worried it's unbelievable -- the amount of weight on my shoulders is killing me," Adlington told the BBC. "It's just going to be such a relief if I do make it. I'm in two very, very tough events and I'm not stupid, I know there are going to be younger girls coming up, everybody's wanting to beat me," added the 23-year-old Adlington. "You have to do it on the day, that's the most scary thing. If you get ill or just fall over the day before and pull something then you've obviously got a tough race on your hands. Eight girls all going for two places and a time -- it is a scary thought."But even if the criteria are not matched by two British competitors in each event, there will be another chance to make the Olympic team at the Amateur Swimming Association (ASA) National Championships in Sheffield, northern England, from June 20-23. Michael Scott, the national performance director for British Swimming, told the BBC: "We don't want tourists -- we don't want to issue any Olympic tourist visas -- we want our swimmers going there at their peak in London in July." Adlington, who confirmed her London gold medal credentials by winning the 800m title at last year's World Championships in Shanghai, said: "There's always going to be pressure leading into the Games but I'm more excited. "I'm really looking forward to it. I hope I qualify - that's the biggest thing, I just want the chance to go and race at my home Games." There will also be an overseas contingent taking part at the UK trials but while heats will be multi-national contests, there will be separate all-British and international finals so as to simplify the business of selecting the British team and ensure none of the local swimmers are over-exposed to potential Olympic rivals before the Games. Germany's Paul Biedermann and Marleen Veldhuis of the Netherlands are among the leading international swimmers at the test event. Teams from France, Spain, Brazil, Poland, South Africa, Sweden and Korea are also due to take part but no major medal contenders from swimming powerhouse nations the United States and Australia, whose trials take place later this month, are expected in London in the coming week.