Starbucks profits fall through the floor so they close shops and move out of the uk, resulting in lost rents, business rates, suppliers and worst of all many people out of work completely.
The demand for coffee shops will still be there, business will simply transfer over to other places that are not in the news getting hammered for shitty treatment of employees. The other coffee shops will employ more people, they'll buy more stock and pay more taxes, and perhaps even open up more coffee shops. Thus equilibrium is maintained.
It's not like Starbucks are the only coffee shop operating in the UK, there are plenty to choose from.