Paper tax returns for the 2008-09 tax year must reach HMRC by midnight on Saturday 31 October 2009. The deadline for paper tax returns is only normally later than 31 October if the tax return or a 'Notice to File' online is received by a taxpayer after 31 July, or there is no software available to file the tax return online, for example in the case of Non-Resident Companies. Tax return submissions online have an extended filing date of 31 January 2010.
If the paper return has a 31 October deadline and is submitted to HMRC after that date, then an automatic £100 penalty will apply. Late Partnership returns attract a £100 penalty for each partner. Late Trust and Estate returns result in a £100 charge to the trust or estate.
Full details of the 31 October deadline are available here