Basically, all it does is adding the "gl=gb" parameter.
After installing this extension, you may want to set "Google UK" as the Default Search Engine so that searching in the address bar will use Google UK. To do so, open the Options page, click "Search" on the left side, and then change the Default Search Engine in the drop-down list. Alternatively, you could just prefix your search with "guk" (without quotes) to search Google UK without changing your current default search engine.
