I’ m looking for a young adult novel set in Wales (or possibly Cornwall), published in the 1940s or early to mid 1950s (based on my age when reading it). I recall a Customs (Revenue) Officer who was trying to stop smuggling, some accusations of witchcraft involving an old woman who was named Granny Shinkin (or something like that) and, at one point, a massive civil disobedience action where many women all dressed up the same and chanted the words in the stumper title to keep the Customs Officer from arresting the old woman.