英国过境签

五月从美国飞回国，有美国F-1签证，买了british Airway的机票，在伦敦转机，不知道要不要过境签证。
刚才看UK Border Agency说'Transit without visa' concession - DATV exemptionsIf you are a national of a country covered by the DATV system, you may be able to transit the UK airside without a visa. To qualify for this exemption:you must arrive and depart by air; andyour onward flight must be confirmed, and must depart within 24 hours; andyou have proper documentation for your destination, including a visa if necessary.Additionally, you must hold:1) a valid entry visa for Australia, Canada, New Zealand or the USA, and a valid airline ticket for travel via the UK, as part of a journey to or from one of those countries; or这么说是不是应该不用过境签证了！？但是心里总是不踏实，有没有实战经验的旅游帮忙解答一下~谢了！！