Summers’ professional career began in the mid-1960s in London as the guitarist for the British rhythm and blues band Zoot Money’s Big Roll Band, which eventually came under the influence of the spreading psychedelic scene and morphed into the acid rock group Dantalian’s Chariot. After the demise of Dantalion’s Chariot, Summers joined The Soft Machine for a period of six months and toured the United States. For a brief time in 1968, he was a member of The Animals, then known as Eric Burdon and the Animals, with whom he recorded one album, Love Is. The album features a recording of Traffic’s “Coloured Rain”, which includes a guitar solo by Summers that runs a full 4 minutes and 15 seconds. The LP also included a reworked version of Dantalion’s Chariot’s sole single “Madman Running Through The Fields”.
After a period of five years in Los Angeles, mostly spent at California State University Northridge in the Los Angeles suburbs, he returned to London with his American girlfriend Kate Lunken. Back in London, Summers recorded and toured with a number of acts, including Kevin Coyne, Jon Lord, Tim Essex, Neil Sedaka and Kevin Ayers. In 1975 he participated in an orchestral rendition ofMike Oldfield seminal piece Tubular Bells.
In 1977, Summers was invited by ex-Gong bassist Mike Howlett to join his band Strontium 90, along with future Police mates Sting and Stewart Copeland.