CASE WHEN in BI Publisher

Summary

Using CASE WHEN in BI Publisher SQL and not getting results

Content

Hi all, I have been writing a BI Publisher data model with SQL to bring back employees along with their ethnicity as well as other fields, my report works and everyone comes back it is just when i go back into my SQL code and try and clean the data up that i am having problems. 

As an example we have data coming back for White-British as A1, so i am trying to write a CASE WHEN Statement to say when ethnicity = A1 then ethnicity = White-British. However the A1 is not changing.