Aren't they amazing?
I have a wee bit of research to follow through on involving the works of the illustrators of this book Anne and Janet Grahame Johnstone, who were quite prolific children's books illustrators in Britain in the 1950's - 1960's and beyond. Their story is amazing, they were twins an up until the death of Janet in 1979 they never solely illustrated a book individually, until that time all their work had been done together. Here is the Wiki link
to their story and a bit of history about them, absolutely worth a few minutes of your time for the read. Some of their most noted work was with Dodie Smith the author of One Hundred and One Dalmatians and Edin Blyton's, The Enchanted Wood which is noted as being one of the twins most collectible works of illustrations.
My online investigations regarding this title, and regarding what dealers are selling this title for have thrown me some seriously crazy results. Let's just say some results indicate I could take myself out for dinner at the local Indian place I love if I sold it at one particular price. However other results indicate that it I could treat myself to a night away somewhere nice. I'm holding out to consult with a vintage/antique book dealer friend of ours. I have however become rather fond of the twins story (being a twin angel mumma myself) and I'm rather fond of holding on to this book and starting a collection of the books they have illustrated.