If you bought the two recent massive Billy Bragg box sets issued in the U.S. by Yep Roc you would certainly own all the Billy Bragg most people would ever need (outside of his collaborations with Wilco). But you wouldn't have everything. Bragg's Peel Sessions CD is currently out-of-print, and for the most part the songs from it did not make it to the box sets, neither did most of the material from the still-in-print Reaching To The Converted compilation.
The Peel Sessions CD is worth hunting for because it contains some stripped down versions of songs from Talking With The Taxman About Poetry and Worker's Playtime, giving you an idea what the songs would have sounded like if Bragg had stuck to his initial "one man Clash" aesthetic.
Bragg's earliest material showed him to be both an effective political agitator and chronicler of heartbreak. But the brutal, heart-on-sleeve honesty of his early songs, coupled with a lack of sympathy for their female subjects, made some of the early songs seem to border on misogyny (e.g. "The Saturday Boy," "The Man In The Iron Mask"). Later material like "Levi Stubbs Tears" and "Valentine's Day Is Over" proved that Bragg could write equally well about heartbreak from the female perspective, and brought an added dimension of empathy and compassion to his work. Listening to this song, written from the perspective of a long-abused woman finally working up the courage to kick her tormentor to the curb, still gives me chills. The lyrics are even more brutally affecting in the stripped down Peel Sessions reading.