An interesting but rarely-known fact about the Union Flag (or “Union Jack”) is that the there are very few laws governing its usage. Technically, the Union Flag is the property of the Monarch, not of the State (or government).
Therefore it is common that instructions regarding the usage of the Union Flag are “commands” issued by the Sovereign, rather than laws passed by the government.
In the UK, there is no Flag Act governing the usage of the Union Flag, and its use is usually governed by long-established customs and traditions, such as dates when the Union Flag can/should be flown (and subsequently dates when other flags should be flown), as well as dates when the government is ‘commanded’ to fly the Union Flag from government buildings (any building used by the royal family, the civil service, or the armed forces).
Flags are typically flown from 8am to sunset, but can also be flown at night, provided they are properly illuminated.