HM Revenue and Customs (HMRC) deadline for 2016/2017 Paper Self-Assessment Tax Return is 31 October 2017. If you fail to meet this deadline then your Self-Assessment Tax Return will have to be submitted electronically as the deadline for Online Tax Returns is the 31 January 2018.
Penalties
Any deadline missed will be amount to a Penalty. The minimum penalty is £100 if your return is up to 3 months late. You may be able to appeal this penalty if you have a reasonable excuse for submitting your Self-Assessment tax return late. Note that a penalty will apply even if you do not owe tax.

Shoaib Aslam is the co-founder of Pearl Chartered Accountants, a UK-based chartered accountancy firm that has multiple locations across London. They are experts in helping startups and established businesses with all aspects of growth, strategy, scaling up, accounting and tax planning.