Brendan, I think the answer to 25A " Frenchman who wrote etc,' was Jean Genet not Jean Jeanie.I failed to see any David Bowie inspired clues. All the best, Setanta1.
Setanta1, "Jean Genet" is a deliberate pun on Jean Genie - in fact Bowie actually named the song as a pun on Jean Genet. The most obvious Bowie reference was the album title at 1a. There was another (indirect) album title at 21 & 23a and a song reference at 9a. Best of all was the positioning of the first four letters of 6a exactly above the first four letters of the second word in 10a - look it up for yourself!
Well, the concealed letters of LIFE in Lifer were immediately on top of those of MARS in Marsh, so it was Life on Mars... just a bit of fun, and obviously a ghost theme that wouldn't have affected anyone who didn't spot it.
PS You may be interested in today's (10 Jan) Guardian and FT puzzles set by Philistine and Goliath respectively (actually pseudonyms of the same setter). But perhaps you may not. ;-)