The very fact that this and this appear on the Adam Smith Institute blog is enough to make me suspicious, but superficially the idea does have its attractions. The publication from the ASI, plunges straight into the Laffer curve. I don't have time to google this but I know that its very existence seems to be hotly disputed.
As far as a flat tax goes I seem to recall a similar idea expressed by Jo Grimond in his autobiography. It has certainly been around for a long time.