Although a wealth of rock encyclopedias exist and nearly all have a small section covering Mott the Hoople and Ian Hunter, there are very few books dedicated to them. It is impossible to do Mott's or Ian's careers justice in only a handful of paragraphs and, sadly, most of these encyclopedias contain errors (mostly minor, but one or two contain major "howlers"). The following are, however, highly relevant to Ian Hunter and Mott The Hoople:
The official biography (as of 2019) is Rock 'n' Roll Sweepstakes Vol 1, which is Campbell Devine's updated Ian Hunter biography covering Ian's formative years up to Mott's split at the end of 1974. Vol 2 will cover 1975 to the present day and is due early in 2020.
Then there is Ian's famous Diary Of A Rock 'n' Roll Star, chronicling Mott's 1972 American tour. This is now (2019) back in print.
2014 saw (roadie) Philip John's You Rocked, We Rolled which chronicles Mott's final European tour with Mick Ronson in October 1974.
2013 saw a massive coffee-table book We've Got A Great Future Behind Us (now out of print).
2013 also saw Overend's long-awaited The Man Who Hated Walking about his walking exploits in 2003.
In the 1990's and early 2000's there were the excellent Outsider and Just A Buzz fanzines, put out by long-time fans Sven Gusevik and Justin Purington respectively (Justin is now joint webmaster for Ian's official website).
1998 saw Campbell Devine's Official Biography. This has now been superceded by Rock 'n' Roll Sweepstakes (see above).
From 1999 to 2011 there was the Mott The Hoople Appreciation Society. Sadly, the MTHAS is no more (and I'm not sure if back issues are still available).
In the mid 1990's there was Phil Cato's disappointing and entirely derivative book.
Of course, there is Willard Manus' novel Mott The Hoople, which inspired the name, from 1966.