How much more difficult would it be for a banker in Britain in say 1850 or 1950 to stow away money in Switzerland compared to today?
Prior to the First World War, capital property and income taxes in the western world were generally lower than they are today, and so the incentive to engage in complicated evasion schemes was less pronounced. Although tax evasion and fraud certainly existed in the 19th century, the modern day scale of this phenomenon is largely a post-1914 creation.
I'm afraid tax evasion is somewhat outside my field of expertise, but I had a word with a colleague who dabbles in this. Helpfully, he came up with a number of texts for further reading, should you be interested in pursuing this subject.
Jogarajan, S.; Double Taxation and the League of Nations (Cambridge Tax Law Series); Cambridge University Press, 2018
Rixen, Thomas; "From double tax avoidance to tax competition: Explaining the institutional trajectory of international tax governance"; Review of International Political Economy, 18(2), 2011: 197-227
Rixen, Thomas; The Political Economy of International Tax Governance; Palgrave Macmillan, 2008
Zucman, Gabriel; The hidden wealth of nations : the scourge of tax havens; The University of Chicago Press, 2015