To find the time in Hong Kong relative to the UK you need to know the time zone of Hong Kong and whether either country is on summer time (also known as daylight-saving time). Hong Kong is eight hours ahead of Universal Time (GMT), and it doesn't use summer time. So it is eight hours ahead of the UK during winter and seven hours ahead during UK summer time. There is no official international register of national time zones. Any country is free to choose and vary its time zone(s) at it pleases. Many published lists contain errors. We recommend the list in the (annual) Admiralty List of Radio Signals, Volume 2, as updated in Section VI of the Weekly Edition of 'Admiralty Notices to Mariners', both published by the UK Hydrographic Office, but note that they use a minus sign to indicate times ahead of Greenwich and vice versa. Current information can also be found in the OAG (Official Airline Guide) held by travel agents.