Well I've just wasted an hour of my life, I've walked the banking from rear of the houses on Stockport Road to Hilltop Drive and including the site of the old shelter but to no avail!!
There are no signs of a tunnel entrance and from memory I hung out in the shelter (on many occasions) in my youth and there were no doors leading out of it other than the entrance / exit!, trust me, if there were I would have been through them.
Any further information would be greatly received and appreciated as I have a few other tunnels in the area that are on my to do list, which exclude the 'well known' ones.