Bathroom Seven-of-Nine

Some weeks ago we lined up Ray the plumber to install a new shower this week.  That was before two other shower-related problems leapt to the fore, so, instead of the one we wanted we get to urgently fix this one.

It may look harmless (for values of 1980's bathrooms) but, for one, that shower is continuously leaking water into the wall - a feature that only became visible when the damp arrived big-time on the other side of the 12 inch wall.  

Ahead of that task though, is finding out where the water comes from and goes to.  There is a stoptap but it's embedded into the wall such that it cannot be turned off, and that cannot be dealt with without first grinding off the handle of the tap...

Here beginneth the adventure.