There is a striking similarity between these boats and the three main boats described in the book “Coot Club” by Arthur Ransome.  Coot club was first published in 1934 so predates Micromodels by a few years.
The wherry is “Sir Garnet“, the motor cruiser is the “Margoletta” and the yacht is the “Teasle“. There are various illustrations in the book that provide information for models. These illustrations could have originated the idea for a set of models.

The Thames Barge from set XI is also featured in the story, it is the “Welcome“.