Nintendo doesn't want Britons to import Advance Wars 2, instead "asking" them to wait the the rest of the year for their version to come out.
When Pokémon Ruby and Sapphire were released in the States on March 17, Nintendo of Europe wasn't all that happy about the relatively high amount of imports finding their way across the Atlantic. Nintendo issued cease and desist letters to infringing retailers that offered Nintendo's GBA games as imports, and for the most part, the situation was resolved.
However, with Advance Wars 2 just recently released in North America, Nintendo is once again worried about a high amount of imports, that it claims will hurt the official launch of the game, and the sales of retailers who sell the game legitimately. The UK arm of the company is again "asking" retailers that offer imports to knock it off, or suffer the concequences.
Advance Wars 2 is set for release in Europe in the late fall, where as the US version was released on June 24.