The EU as a whole is the biggest trading bloc in the world, obieone. It stands to reason that the UK will have more clout being part of that group rather than standing on its own.
Many of the top wealthiest countries are wealthy because of their financial centres, not trading goods. Switzerland springs to mind, along with Lichtenstein and Luxembourg.
"Twelve of the 25 richest countries are in Europe, while the US and Canada also made the cut. The UK did not make the top 25, ranking at No. 27 with a GDP per capita of $39,224 (£27,241).
Some small countries, such as Liechtenstein, Nauru, Vatican City, Monaco, San Marino, and Andorra were not included in the study.
The GDP per capita listed represents the amount of wealth produced in 2015 and is expressed in international dollars."
According to Business Insider magazine, 12 of the 25 richest countries are in Europe. Last year's figures.