The passage highlights that despite a decrease in the value of English exports post-Second World War, England's national prosperity has increased, indicated by higher incomes for various low-paid workers. This suggests that traditional measures of economic prosperity, like exports and trade balance, do not fully capture national prosperity.
The key emphasis is on the improved income levels of average citizens rather than trade figures. This strongly supports the statement that "a country’s economic standard can be best adjudged by per capita income." The passage argues against using balance of trade and export growth as sole indicators of economic prosperity and instead points to the importance of income levels of the general population.
Hence, based on the passage, the most supported statement is: "a country’s economic standard can be best adjudged by per capita income."