If you start with an empty database (instead of with AlloyTech), there shouldn't be any pages at all in your database. Then, make sure you have your settings for languages correct before you create the very first page.
If you have created a content in wrong language branch and you need change master language for all content there is a Sql script for this (not sure if this is officially supported). Some roots are here (login required) - https://www.coderesort.com/svn/epicode/EPiCode.LanguageTool/EPiCode.LanguageTools/ChangePageBranchMasterLanguage.sql
Otherwise you need to install empty site and enable only UK English language.
Currently, when I create a new EPiServer 6 R2 site, the pages are US English and the only other enabled language is Swedish. I have to mess about removing pages, adding UK English and adding new UK English pages.
Is there any way of creating a new site with the UK English language as the default and with UK English pages?