I’ve received a letter from the Taxman asking for my tax return for the year 5 April 2010 to be submitted. But I submitted that tax return in September 2010, and I’ve paid all the tax due for that tax year. Do I have to submit that form again?
No. The letter you have received from the Tax Office is a mistake. About 40,000 of these standard letters (Notices SA316) have been printed with the wrong tax year: 2009/10 rather than 2010/11. You should receive another notice SA316 asking for the tax return for 2010/11, and a letter of apology concerning the mistake.