Those who don't file their tax self-assessment forms for the 2008/09 tax year by 11.59pm on 31 Jan (a Sunday) face an initial £100 penalty plus interest on late payments.

Here's an urgent Q&A on what to do:

Q. Who needs to file a return? A. Those whose tax is deducted by their employer usually DON'T need to submit a form. Yet the rule's simple: if you've been sent a self-assessment form you must submit it. Those who haven't been sent one but have any extra income from self-employment, some investments or savings (as a higher rate taxpayer), have a duty to tell the revenue (0845 900 0444).

Q. Why may I need register TODAY? A. The deadline for filing by post was 31 October, so to avoid a fine you must file online. Yet if you've never filed online you need to register, and it can take seven working days to get your code, so do it ASAP. To register, go to the HMRC website and read the Last chance filing online MSE news story. There's no need to re-register if you've previously filed a web-based return.

Q. What if I I'm owed tax BACK? A.You may be due £100s of tax back if, for example, you've only worked part of the year, or are a non taxpayer who paid tax on savings interest. See the Revenue's refund forms. For the self-employed, remember you only pay tax on profits after legit expenses, so claim back all you're entitled to (see the Revenue's allowable expenses).

Q. Where can I get free help? A. You can ask the revenue for advice, yet there are also a host of charities and agencies that give help completing forms, especially for those on lower incomes. See the Free Tax Help note.

Further reading/Key links

Tax help: 2009/10 Tax Breakdown, Taxing Times