Seligman on Income Tax

A copy of ERA Seligman's The income tax : a study of the history, theory and practice of income taxation at home and abroad is available here at the time of writing.

Income Tax Acts (1799-1952)

The older UK Income Tax Acts are not that easy to find online, but these links work as at the date of posting.  No joy on 1918 yet.

Income Tax Act 1799
Income Tax Act 1803 (at p. 1012)
Income Tax Act 1842
Income Tax Act 1952