I'd not come across the word snicket (except in the Lemony Snicket books my kids used to read) until my musical partner Margaret used it. She's from Ilford and had picked up the word from her sister who lived for a time in Selby where it seemed to be used in the same way that redhorse mentions. Like redhorse Margaret hthought it sounded like a "sneak-it" and now uses it to refer to any little short cut. When we're driving to a gig if I'm told to "take the snicket on the left" I know I have to look out for a little alleyway rather than a main road.
I find this thread so intriguing we might have to work it into one of our songs: "Through snickets and through ginnels/I lately took my way..."