A degree of political support is growing in Europe for some form of tax on financial transactions, with the French president, Nicholas Sarkozy and the German chancellor, Angela Merkel, backing the plan at a summit in Paris on Tuesday.The two heads of government did not spell out any details of their vision for the tax, but said their finance ministers would outline a proposal for such a tax next month.Over the years, plenty of schemes have been floated for small taxes on foreign exchange transactions, securities trading and derivatives. Proponents claim such taxes might prove an effective means of raising additional tax revenue, though the merits of these schemes are uncertain.Calls for such taxes have been more common since the financial crisis gathered momentum four years ago.The Financial Times' Alphaville blog points out that Sarkozy has called for transaction taxes in the past, noting the "only difference now seems to be that he's looking to use the proceeds to prop up the eurozone rather than to fund development in Africa and climate change mitigation efforts."