I’m looking for a British book written probably between 1946 and 1953. About a group of teenagers and a professor who escape world apocalypse by petrification in a balloon. They travel all over the petrified world and visit the USSR where they topple Stalin’s petrified soldiers like dominoes. I remember thinking the book to be very gory for a children’s book. My Mom read this book when she was a teenager and said the author was fairly well known in Britain at the time.