31st October 2016 is the filing deadline for filing a paper tax return under self assessment. It is also the deadline:

If you want to benefit from transitional relief on investment growth from a disguised remuneration scheme: you have to register your interest to settle with HMRC by 31 October 2016.

And, remember remember the 5th of November...

Don't forget to file your Employment Intermediaries quarterly return, see Agency workers: employment intermediaries rules

For more deadlines see Deadlines: compliance (individuals and companies).