it did change this year, PAPER returns now need to be in by 31 October, but online returns have until 31 Jan. From hrmc website
Tax return deadlines and late return penalties
31 October: Paper returns
If you are sent a notice to complete a tax return before or on 31 July and you want to send us a paper return you must send the completed return back by 31 October.
If you are sent a notice to complete a tax return after 31 July you must send the completed paper tax return back by the later of 31 October or three months following the date of issue of the notice.
For paper returns that reach us by this date we will:
calculate your tax for you (though you can calculate it for yourself if you want)
tell you what to pay by the following 31 January
collect tax through your tax code (if possible) where you owe less than £2,000 unless you tell us otherwise.
If the paper return arrives after this deadline you'll be charged an automatic £100 penalty.
(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.)
(There are a very few cases where online tax returns can't be made. In these cases the deadline by which the paper return must reach us is 31 January. See 'Deadlines for tax returns that can't be sent online' below.)
30 December: Online returns (for tax to be collected through your tax code)
If you send us your tax return online you must send it back by this date if you want us to collect tax through your tax code (if possible) where you owe less than £2,000. Otherwise you can send it to us up to 31 January.
31 January: Online returns
Where a notice to complete a tax return is issued before 31 October this is the deadline for sending back an online tax return.
Where a notice to file a tax return is issued after 31 October the deadline to send it back is three months after the date of issue of the notice.
If it arrives after this deadline you'll be charged an automatic £100 penalty.
(This is also the deadline for paper returns where there isn't the option to file the return online. See 'Deadlines for tax returns that can't be sent online' below.)
(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.)