SA100, SA109 and split year treatment

I would like to ask if for late submission of SA100, SA109, spilt year treatment, for SA100, the deadline for online is 31 Jan 2023, is the online submission function supports late filing after 1 Feb 2023? while submitting SA109, i need to file SA109 and apply spilt year treatment, but SA109 is not supported by online submission, do I need to submit my SA109 by paper together with the SA100 by paper together? or I can submit via a third party software even deadline is passed?

Hi,

There are some areas of Self Assessment that require the use of third party software to submit the return online, such as residence.  

The following guidance advises when you cannot use the online service and the options available of purchasing third party commercial software or printing of a paper tax return and posting it.  

File your Self Assessment tax return online

Paper tax returns received after 31 October each year are considered late, as are online returns received after 31 January.

Thank you.