HMRC has published a blog listing its top 5 most popular self assessment questions, with answers.
Just a word of warning to those less familiar with personal tax in relation to the answer question 2.
When you fill in a tax return online, HMRC’s software does indeed automatically work out and display how much tax and Class 4 National Insurance contributions you owe. What it does not do is show the deduction for the payments on account which you may have already paid on 31 January 2017 and 31 July 2017. So do be careful to make sure you are reading, and paying, the correct amount.