Stamp Duty is a tax on share transactions in the UK. It makes dealing more expensive than it otherwise would be, and therefore increases inefficiency in financial markets.
It also creates discrimination between stock markets as it is possible to trade UK shares on overseas stock markets without paying stamp duty (and such markets, even in the rest of Europe, typically do not have such taxes).
UKSA would therefore like to see stamp duty, which is after all a relatively minor source of tax revenues, removed altogether.