Spain was born in Jesmond, Newcastle upon Tyne. She was the second of the two daughters of Lieutenant-Colonel George Spain, a freeman of the city and a prominent figure in local military and antiquarian affairs. He was a writer himself and appeared in a number of radio plays as well as broadcasting commentaries on Newcastle United games. Her mother, Norah Smiles, was the daughter of Lucy Dorling (a sister of Isabella Beeton) and William Holmes Smiles (son of Samuel Smiles).