Most of the items in this photo are 1:76 OO scale models of English trains, except:
second shelf, two items at left are HO Sydney commuter cars.
third shelf, brown-and-cream car is HO, compare to OO versions of similar-style English cars on same shelf.
fourth shelf, diesel at left is HO painted for Victorian Railways.
HO scale models of English railway stock look noticeably smaller than American HO because of the smaller English loading gauge. OO scale bulks them up to a similar height and width, which in earlier years helped to fit available motors in the locos (according to references).
OO scale models of English passenger cars make them about the right size to resemble some older Australian passenger trains in HO. These mostly English-made trains in the photo were gifted to me from a friend in Australia, where modelers often made do with foreign-prototype models. Some of these passenger cars were repainted to cover up the original English markings.
English OO scale uses HO gauge track which equates to 4'1.5" gauge. This disparity has been explained in historical context: