The date of submission of the accounts depends on whether you operate as a sole trader or limited company business,
Sole Trader: taxable income is calculated on an April to April basis and should be sent to HMRC, via the self assessment tax return, before the following 31st January. So the 5th April 2012 tax return is due 31st January. If the tax return is submitted by paper this date is earlier.
Limited Company: this date can vary from one company to another and is dependent on the account year end period of the company. The accounts are due at Companies House 9 months after the year end and 12 months after with HMRC.