JLB's primarily employees featured in Peep Show are Mark, Sophie, Jeff, and later Gerard. Johnson is shown to have joined JLB at their superior in the Series 1 episode Mark Makes a Friend, but in the episode Dance Class, at the beginning of Series 2, the employees are shown celebrating that Johnson is now their official boss and the manager of their entire branch, presumably replacing their previous boss in Series 1, Barbara.
Jeremy and JLBEdit
Jeremy gets an interview at JLB (which he fails at) in the episode The Interview in Series 1. Eventually, he gets a job at JLB, which is shown in the episode Jeremy at JLB in Series 6, although Jeremy only works at JLB for a few hours before the branch is closed down.
At the beginning of Series 6 in the episode Jeremy at JLB, Johnson announces that the branch is being shut down. This leads to Mark getting a job as a Mexican restaurant waiter and a historical walking tour guide, and writing a satirical play about the German branch of JLB which was rumored to cut off the London branch to "save the mothership", even though the London branch was performing well. The shutdown also led to Johnson slowly losing his mind and founding a startup called Consultio/Consultius.