The band have since claimed that the success at Sunbury was a result of their persistent touring, which had generated a grassroots following who had all assembled at the festival and encouraged the rest of the audience. Cornick recalled, "from that moment on, we were a big band".
The group recorded their first album, This Was, between June and August 1968, and it was released in October, reaching number 10 in the charts. In addition to original material, the album included the traditional "Cat's Squirrel", which highlighted Abrahams' blues-rock style, while the Rahsaan Roland Kirk-penned jazz piece "Serenade to a Cuckoo" gave Anderson a showcase for his growing talents on the flute. The overall sound of the group at this time was described in the Record Mirror by Anderson in 1968 as "a sort of progressive blues with a bit of jazz".
Following the album's release, Abrahams left the band in December to form his own group, Blodwyn Pig. There were a number of reasons given for his departure. Abrahams had heard that Ellis wanted Anderson to be the frontman and group leader, at his expense, and realised he was unlikely to have the majority share in songwriting. Other reasons given were that Abrahams was a blues purist while Anderson wanted to branch out into other forms of music, and that Abrahams was unwilling to travel internationally or play more than three nights a week. Abrahams himself described his reasons more succinctly: "I was fed up with all the nonsense, and I wanted to form a band like Blodwyn Pig."