According to his biography ("Billy Bragg: Still suitable for miners" by Andrew Collins), the British singer-songwriter left school to work for Overseas Containers Limited (OCL) in London ("at the other end of the A13" so presumably the Barking containerbase office). The book describes his job as involved the processing of insurance claims. Billy left OCL after six months, but on the basis that he was 16-17 at the time we are presumably looking at his time as a former colleague as being around 1973-74.
Billy Bragg (full name Stephen William Bragg) started his music career in 1976 with his first album, Life's a riot with Spy Vs Spy, being released in 1983. 30+ studio, compilation and live albums have followed. His awards have included the AIM Independent Music Awards’ Outstanding Contribution To Music prize in 2013.