Right, so I've been around the entire set of buildings and the meters themselves, Josh, but apart from walking along the rails at WP station, I can't see a way in. I did go through Sir Joseph park's alley way and follow that really, really long mud trail for ages, but I just reached a brook, and even if I was happy wading through it, there was a 10-odd foot high barbed wire fence in the way.
I've just made this account, so I got a chance to glance at the rules and it says asking about/ sharing details on how to enter places is taboo, apparently. Still, hopefully you can help.
Maybe we could meet and do it together - I'm very local!
Cheers.