The Self Assessment tax return deadline for all paper returns is 31 October 2014. If you do not file your paper tax return by this date you must file your tax return online by 31 January 2015 not to receive a penalty.
HMRC have incorporated a new penalty regime which came into effect for all tax returns filed late. Late filing of tax returns can now incur penalties totalling more than £1,600. For tax returns that are one day late the penalty starts at £100, even if there is no tax to pay or if your tax has been paid in full at 31st January 2015.