Even if you haven't heard of Shire Pharmaceuticals or their ADHD drug, Adderall, which they describe as the "leading brand in the US market" you should still be very concerned at the possibility they might leave Britain due to high levels of tax, as is reported in City Am. This is a FTSE100 firm, one of the biggest in the UK. High tax rates won't raise much revenue if firms like this one leave the country.
High levels of tax have hurt our international competitiveness but, although big companies have left before, this is usually hidden by the fact that it is new investment that goes elsewhere rather than existing companies in the UK leaving. Now it is becoming more apparent than ever that Britain's long term prosperity is being imperilled by an increasingly uncompetitive tax system.