This tunnel used to bring hot water under the River Thames from Battersea Power Station on the other side.  
With Battersea Power station just a shell they create their own hot water from big engines that generate electrickery.
 
Yes, yes, onwards…

 
There’s a great big hole with oily water at the bottom. Stuart will probably want one of these at the bottom of his secret underground lair.

 
There’s a great big tower containing hot water, after 7 long ladders the view from the top.
   

Big boilers. Dave approves of the blue and yellow colour scheme.

  
Dave is now in control of the heat for 3000 homes…

Everything up to pressure.