Jethro Tull started their debut as a blues band with the album "This Was" in 1968. Even though the album was an instant success by reaching number 10 on the english charts, it does not contain many hits.
"My Sunday Feeling" and "Some Day The Sun Won't Shine For You" are both characteristical Jethro Tull blues from the early years. Only "A Song For Jeffrey" was released as a single but was not able to enter the single charts. "Serenade To A Cuckoo" was acording to Ian Anderson the first melody he learned to play on flute.
You should also pay attention to "Dharma For One" which opens with a strong flute solo.