Complex sentence: Formed in London in the 1970s it has had a sporadic existence ever since, disbanding in the 80s then reforming and continuing to record and perform through the first decade of the 21st Century.
Split into simpler sentences: Formed in London in the 1970s, it has had a sporadic existence ever since, disbanding in the 1980s then reforming. The band continues to record and perform through the first decade of the 21st century.