"Lhude sing cuccu", better known as "Sumer is icummen in", was written at Reading Abbey, probably at the end of the 13th century, but is in a manuscript in the British Library, MS Harley 978, f. 11b. [The Britsh Library used to have, and may still, a reduced facsimile of the song as a postcard that they sold. I've got one I got there in 1972.]