Written and first recorded by Kristy MacColl (1979).
Hit version by Tracey Ullman (UK #2 1983 |US #8/MOR #11 1984).
Also recorded by Anja Niskanen (1984), Ben Gibbard (2010).
From the wiki: “‘They Don’t Know’ was written by Kristy MacColl, who recorded it in 1979. It became popular on radio in the United Kingdom, reaching #2 on the Music Week airplay chart. However, complications involving a strike at her record distributor prevented the single from being shipped and promoted properly. MacColl’s version of ‘They Don’t Know’ thus failed to appear on the official UK Singles chart, which is entirely sales-based.