These cover south and central Hampshire, including Southampton, Winchester, Alresford, Brockenhurst, Eastleigh, Lymington, Lyndhurst, Romsey and Stockbridge.

The SO area originally had both single and double-digit postcode districts.

[4] In the early 1990s, a shortage of available postcodes occurred due to increased demand.

[5] On 1 December 1993 Royal Mail took the step of dividing each of the existing single-digit districts, the numbers of the new subdivisions containing two digits rather than one.

Whilst this created thousands more possible postcode combinations, it resulted in the unusual situation where the centre of the postcode area, Southampton, lacks a district numbered 1.