Although the Chapel of St. Mary Undercroft in the crypt survived, it subsequently underwent extensive reconstruction by architect Edward Middleton (E.M.) Barry in order to bring it more in line with the Victorian Gothic style, as well as to return it to its former use as a chapel.
"The Crypt under old St. Stephen's Chapel, Westminster, now in course of restoration" (1859)
UK Parliament's flickr Photostream
Antiqua Print Gallery
Lawrence OP's flickr Photostream
Art in Parliament
Guide to the Palace of Westminster. London: Warrington. 1911. 53-54.
Layard, A.H. "Introduction," Paper on Mosaic Decoration read at a meeting of the Royal Institute of British Architects, London: Metchim and Son, 1869. iii.