Valerie and Mary Glassborow were children of Frederick Glassborow and Constance Robinson .
Michael 's mother , Valerie Glassborow ( 1924 -- 2006 ) worked at the Second World War Government Code and Cypher School ( GC&CS ) in Bletchley Park , along with her twin sister , Mary .
Valerie Glassborow and Mary   were children of Frederick Glassborow and Constance Robinson .
Michael 's mother , Valerie Glassborow ( 1924 -- 2006 ) worked at the Second World War Government Code and Cypher School ( GC&CS ) in Bletchley Park , along with her twin sister , Mary .