There is not a song bearing the name "Manchester Maggie" on any of the albums listed on the discography page of the Houhton Wavers' website, or any logical name derived from the lyrics provided that I could find. You could try contacting them at their website.

In the mean time you can listen to a rendition of it here: https://www.youtube.com/watch?v=7nSOCUl_VWk