I have always advocated for a tax on stock trades as a tool to slow speculation (moving money in and out of stocks for the purpose of making a profit) and encourage investment (buying and holding).
Bubbles are caused by speculators.
Why would a tax stop speculation? All that will serve to do is enrich the government. That’s all that taxes do. And the government in Brussels is corrupt enough without this tax to underpin their misdeeds; not once in its existence has its auditors signed off on its budgets.
The only purpose for this tax is to undermine London’s financial sector. It has no other purpose.