The Self Employed are a voter group.
Self-employed people run their own business and work for themselves. Typically, these businesses are small and very sensitive to taxes and regulation, so reducing or eliminating both these threats are the primary concerns for the self-employed.
Policies which help small businesses earn money - such as an Enterprise Investment Scheme and Small Business Grants - will persuade more people to become self-employed. Policies which add expenditures or bureaucracy to small business management - like a Capital Gains Tax and Work Safety Laws - will dissuade people away from self-employment.
The desires of self-employed people to cut taxes and economic regulations naturally sync up well with the free market ideals of capitalists and the wealthy, while frequently upsetting socialists and trade unionists.
The self employed don't have their own pressure group.