Hi. My name is*****'m looking at your question now and will post my answer or ask for more information here in a short while.
Are you still working for a Singapore based employer? Have you returned to the UK permanently or will you be resident in the UK in the 2017/18 tax year?
It was good to chat with you.
You might refer to section 5 in RDR3 here, the notes on split year treatment here and the flowchart here for information on split year treatment.
Provided that you are treated as resident in the UK for 2016/17 and you meet certain other criteria you should qualify for split year treatment so that the 2015/16 tax year is split into two parts, the first running from 6 April 2015 to the day before your return to the UK and the second running from the date of your return to the UK to 5 April 2016. Your foreign earnings and savings should be free from UK tax.
As you returned to the UK in December 2015, under the split year treatment rules the number of days that you will be allowed to spend in the UK and retain definitive tax free status for your foreign earnings in 2016/17 up to the date of your permanent return will be reduced from 90 to 67. See Table F on page 60 of RDR3. You need to qualify for split year treatment under one or more of Cases 4 to 8. See pages 59 to 69 of RDR3.
Call HMRC on the number here or here to get a self-assessment tax return SA100 issued to you. Ask for the supplementary employment pages SA102, the supplementary self-employment pages SA103 and the supplementary SA109 residence pages. See the submission deadlines here.
I hope this helps but let me know if you have any further questions.
Correction: foreign earnings in 2015/16 not 2016/17
Link to SA109 pages here.