必然要签证。
If you will arrive on a flight, remain in the arrival lounge of the airport without passing through immigration control, and then depart on another flight from the same airport, you should apply for a direct airside transit visa.
If you will arrive in the UK, pass through immigration control and then leave the UK within 48 hours, you should apply for a visitor in transit visa. http://www.ukba.homeoffice.gov.u ... ransitthroughtheuk/
上面是使馆的官方解释。
不出机场就是visa to transit airside,下面是签证需要的材料。 http://www.ukba.homeoffice.gov.u ... sa-transit-airside/
拿到签证绝对不超过5个工作日,一般两三天就ok。签证费(拒签不退)70欧元。 推荐你不要考虑签这个签证,争取保险那边退费吧……