One of the mysteries of the English language finally explained.
1The flashing lights and siren used on a police car or other emergency vehicle when responding to an incident. Also later "on (also under) blues and twos".
2The emergency services (frequently the police).
1980s; earliest use found in Autocar. From the plural of blue + the plural of two, with reference to the blue flashing lights and (typically) two-tone siren used on an emergency vehicle.
blues and twos/ˌbluːz ən(d) ˈtuːz/
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