Have a look at the Roud index on the EFDSS website at http://library.efdss.org/cgi-bin/query.cgi?cross=off&index_roud=on&access=off . You'll find a handful of references to songs collected in Middlesex, but a cursory glance reveals 3 main sources: - recordings made by Ken Stubbs, some released as a Topic LP of the Willett family, and some published in his book 'Life of a Man' - Lucy Broadwood's 'English County Songs', published in 1893 - Songs collected by Sharp, some published in journals or by Roy Palmer
And then there are a few noted by other collectors.