Julia Philips wrote a biography of her, Madeline Montalban: The Magus of St. Giles, published in two hundred copies by Neptune Press (that is, Atlantis Bookshop) in 2012 (reprinted in 2015). She was born in 1910 and died in 1982.
To the best of my memory, her writings have only been available directly from her Order of the Morning Star. See https://www.sheridandouglas.co.uk/oms/ There is a little more about her available writings at the back of Julia Phillip's biography.
For her, Lucifer (the name means light-bringer) was not Satan, but an angel also named Lumiel, and her magic seems to have been angel magic in the Hermetic tradition.
She's a major figure in the history of 20th-century British esotericism.
Re: Madeline Montalban's Order of The Morning Star and associated material
To the best of my memory, her writings have only been available directly from her Order of the Morning Star. See https://www.sheridandouglas.co.uk/oms/ There is a little more about her available writings at the back of Julia Phillip's biography.
For her, Lucifer (the name means light-bringer) was not Satan, but an angel also named Lumiel, and her magic seems to have been angel magic in the Hermetic tradition.
She's a major figure in the history of 20th-century British esotericism.