Complex sentence: Although he had a private income, Lethbridge ended up becoming the keeper of Anglo-Saxon antiquities at the museum, and he remained in Cambridge until 1957, bored with what he called "the academic trade-unionism" that existed within his profession.
Split into simpler sentences: Although he had a private income, Lethbridge became the keeper of Anglo-Saxon antiquities at the museum. He remained in Cambridge until 1957, bored with what he called "the academic trade-unionism" that existed within his profession.