Not sure if anyone remembers this post, but it is still situated near to where I live even though the visitor centre has gone. One of the people on a local Merseyside forum is part of an urban exploration group and he and a few others managed to gain access inside the sub...I have included the link which includes some of the pictures for anyone to take a look if they want to plus a link from the actual urban exploration web site too
Enjoy!!
Dave
http://www.yoliverpool.com/forum/showthread.php?t=6019
http://www.level-two.co.uk/u534.php