Apologies if this isn't a to level answer, but I want to address the question of Belgian stereotypes.

Arguably the most famous fictional Belgian in the anglosphere, but certainly the most famous fictional Belgian created by a non-Belgian, is Hercule Poirot. Agatha Christie published the first Poirot story in 1920, exactly the timeframe you are asking about. I don't recall is there are any depictions of him eating or drinking but he certainly talks to people from other countries. Although this the work of a single author and is therefore an idiosyncratic depiction of a Belgian stereotype, it will give an insight into a British perspective from that era.

Source: many Poirot novels and short stories by Agatha Christie