What Was Lost Was Lost" was the winner in the first novel category of the Costa Book Awards. O'Flynn received a £5,000 prize. It was short-listed for the overall Costa Book of the Year Award. The Costa Book Awards' judging panel, chaired by Joanna Trollope, praised the novel for "blending humour and pathos in a cleverly constructed and absorbing mystery." They described the novel as inventive, compelling, and poignant. "What Was Lost" was long-listed for the 2007 Man Booker Prize and the Orange Prize for Fiction. It was short-listed for the Guardian First Book Award. It won the Jelf Group First Novel Award
Nestlé Smarties Book Prize with no single prize). Silver and bronze runners-up in each category were introduced in 1996 and designation of one overall winner was abandoned at the same time Eligible books were written by UK citizens and residents and published during the preceding year (not precisely the calendar year). The shortlists were selected by a panel of adult judges, finally chaired by Julia Eccleshare, children's books editor for "The Guardian". First, second, and third places were determined by British schoolchildren—at least finally, by vote of "selected school classes" The prize was discontinued in 2008 by what was described as a "mutual" decision