A sharply rising number of attempts to block imports has led to a much smaller increase in actual tariffs and affected only a limited share of global trade, according to World Bank research.

The latest results from the Global Antidumping Database , a monitoring service sponsored by the bank, show the number of new official investigations into imposing so-called "trade remedies" - which are, in reality, emergency blocks on imports - rising sharply in the third quarter of 2009.