The copy of the Kelmscott Chaucer once owned by Freeman Bass and later by his son B. Bass (Census 2.7) will be sold by Bloomsbury Auctions, Important Books and Manuscripts, 15 May 2012, lot 44. The book is in a plain white Sangorski & Sutcliffe binding, slightly soiled. The estimate is £30,000–40,000.
The online catalogue is here.
[Update, 2 June 2012: The book sold for £25,000 (not including premiums).]