Tax return (United Kingdom)
In the United Kingdom, a tax return is a document that must be filed with the HM Revenue & Customs declaring liability for taxation. Different bodies must file different returns with respect to various forms of taxation. The main returns currently in use are:
- SA100 for individuals paying Income Tax
- SA800 for partnerships
- SA900 for trusts and estates of deceased persons
- CT600 for companies paying Corporation Tax
- P35 for PAYE deductions by employers and National Insurance contributions
- VAT100 for value added tax
Income tax self-assessment
Most employees paying tax under the PAYE system are not required to file a tax return, because the PAYE system operates to withhold the correct amount of tax from their wages or salaries.
A tax return is required for
- the self-employed including someone in a partnership
- controlling company director, but not a director of a non-profit organisation or anyone not receiving any payments or benefits
- a minister of any religion
- a name or member of Lloyd's
- income from savings and investments of £10,000 or more
- income from untaxed savings and investments of £2,500 or more
- income from property of £10,000 or more before deducting allowable expenses or £2,500 or more after deducting allowable expenses
- employment income on PAYE above £100,000
- anyone lived or worked abroad or aren't domiciled in the UK
- have Capital Gains Tax to pay
- anyone who owes tax and it can not be collected through the tax code. For instance when the taxable Basic State Pension is greater than the Personal allowance
- anyone who has benefits in kind or out of pocket expenses which may be taxed as an employer does not have a dispensation
The standard form in use is the SA100, complete with additional sheets for particular sources of income. A short tax return, form SA200, is available for those with incomes below £30,000. HMRC selects those that can complete a SA200.
The tax year runs to 5th April. These tax returns must be completed by 31 January following the end of the relevant tax year for those who complete the tax return online and by 31 October following the end of the tax year for those who file by a paper return. 
A partnership, including one in which all partners are companies, files form SA800. The partnership itself does not normally pay income tax, capital gains tax or corporation tax, but is required to provide a Partnership Statement to each partner reporting that partner's share of income and gains.
Trusts and estates
A trustee, including trustees of certain pension schemes, must file form SA900 by 31 January following the end of the relevant tax year for those who complete the tax return online and by 31 October following the end of the tax year for those who file by a paper return. A personal representative administering the estate of a deceased person must file a form SA900 if the affairs of the estate are complex. Whether or not a tax return is required, each beneficiary's share of taxable income is reported to the beneficiary on form R185.
Corporation tax self-assessment
A company must file a return, using form CT600, and assess its liability to tax, normally within 12 months of the end of its accounting year.
At the end of the tax year, after 6 April, employers operating PAYE schemes must report to HMRC their employees, the total that has been paid to them, the amounts of income tax and national insurance contributions (NICs) that have been deducted from those payments, and the amount of employer's NICs due. This is done on form P35.