Sole traders and partnerships may need to pay a second installment of income tax for the year ended 5 April 2016 by 31 July 2016, which is the end of this month. You should have received a payslip and envelope through the post by now.
Sole traders and partnerships are collectively known as unincorporated businesses. A few partnerships are set up as Limited Liability Partnerships. These are treated in the same way as other partnerships for income tax purposes, but they need to file their accounts at Companies House as well as filing a tax return. There is also the very rare Limited Partnership, which is also treated like a partnership for income tax, but it does not have to file its accounts since it has at least one partner with unlimited liability.