The sign of the impact on value added is bound to be positive in a closed economy, but in an open economy imports of insurance services may in principle reverse the sign of the impact on total value added in the economy.

In particular, it claimed that although the product concerned was a small part of the importers/traders overall activities, it had a substantial positive effect on their total costs and turnover due to the economies of scale of importing larger quantities of different kinds of coal products, including foundry coke.