Bogwoppit, Paperback/Ursula Moray Williams

When Aunt Lily marries the lodger and goes to America, orphaned Samantha is packed off to her Aunt Daisy, who lives in a grand house at the Park. Snooty Lady Daisy Clandorris has no time for children. Lucky for Samantha, then, to discover the small, furry creature living in the cellar; a bogwoppit - believed extinct - up till now...