Double barrelled names are usually the Victorian equivalent of the Olde English pre 7th Century personal compound names such as 'Ead-Ric', which translates as 'prosperity - powerful'. These names have individual meanings but not when conjoined. In this case, Barrett is Olde French, deriving from 'Barat' or 'Barrette' and being either a metonymic for a maker of caps and bonnets, or possibly a nickname for a Merchant - one who deals in commerce particularly cloth. The name 'Derye' is a variant spelling of the Olde French 'Daree' which means 'A Penny-worth' and again was a nickname for (probably) an inspector of weights and measures. It can also be locational and derive from the Gaelic 'Doire' as in the city of Derry - meaning 'The Oak Trees'. The first recorded spelling of the family name is shown to be that of Robert Barate, which was dated 1165, The Pipe Rolls of Northamptonshire, during the reign of King Henry II, The Church Builder, 1154 - 1189. Surnames became necessary when governments introduced personal taxation. In England this was known as Poll Tax. Throughout the centuries, surnames in every country have continued to "develop" often leading to astonishing variants of the original spelling.