There have been a lot of articles in the press about the lack of tax paid by large multinational corporations in the UK. Quite apart from the fools who don't know the difference between turnover, revenue and profit there is generally a misunderstanding of what corporation tax is meant to be taxing. This article explains it, http://www.ifs.org.uk/publications/8132 .
Having digested that, now take a look at this article, http://fullfact.org/economy/google-paying-3-tax/ . To its credit it explains where the figure of 3% comes from. What is depressing is the comment by the Public Accounts Committee that says "Google relies on the deeply unconvincing argument that its sales to UK clients take place in Ireland". Since you will have now read the first article you will understand how this quote more than adequately demonstrates how disingenuous our politicians can be.