After a little more research and some input from readers i’m now confident these are the remains of a QF decoy site called Greenabella. These sites lit controlled fires during air raids to appear as targets struck by bombs. This location was a civil decoy for Middlesbrough.
I think the larger structure with the holes for pipes and a chimney is likely to be the generator building, with the smaller structure the shelter.
Other decoy sites in the area also have unusual structures.