Self defined ethnicity (SDE) codes are a set of codes used by the Home Office in the United Kingdom to classify an individual's ethnicity according to that person's self-definition.

The codes are also called "18 + 1" codes, as there are 18 of them, plus one code (NS) for "not stated".^[1] In addition to the previously used 16+1 codes, they contain the categories W3 and O2, while A4 is now replacing O1 (Chinese).^[2]

The code system originated in the United Kingdom Census 2001 based on Recommendation 61 of the Stephen Lawrence Inquiry Report (SLIR).^[2][3]

British police forces are required to use the SDE 18+1 codes (as opposed to the commonly used radio shorthand IC codes) when spoken contact has taken place and an individual has been given an opportunity to state their self-perceived ethnicity.

White

• W1 – British
• W2 – Irish
• W3 – Gypsy or Irish Traveller
• W9 – Any other White background

Mixed or Multiple ethnic groups

• M1 – White and Black Caribbean
• M2 – White and Black African
• M3 – White and Asian
• M9 – Any other Mixed or Multiple background

Asian or Asian British

• A1 – Indian
• A2 – Pakistani
• A3 – Bangladeshi
• A4 – Chinese
• A9 – Any other Asian background

Black, Black British, Caribbean or African

• B1 – Caribbean
• B2 – African
• B9 – Any other Black, Black British or Caribbean background

Other ethnic groups

• O2 – Arab
• O9 – Any other ethnic group

Not stated

• NS – Not Stated.

• Classification of ethnicity in the United Kingdom
• IC codes

• Ethnicity facts and figures. Government data about the UK's different ethnic groups.