Night boxes were a service of post office boxes offered by the British Post Office at some major sorting offices during the inter-war years. Such boxes were available to callers to collect mail during the night hours when the boxes were normally closed to callers, at double the rent of normal boxes. Letters to such boxes had to be sent in red envelopes clearly marked "Special Private Box Night Delivery".
References
- Post Office Guide - Page 46 Great Britain Post Office - 1920 "Under this arrangement a Renter of a Night Box can, during the hours of attendance of the Night Staff, obtain letters arriving after the office is ordinarily closed to callers, which otherwise would not he delivered until next morning. Such letters must be enclosed in red envelopes"