NEWCOMERS to tax self-assessment need to register for online filing as soon as possible to meet the January 31 deadline and avoid an automatic late filing penalty.

If any tax is outstanding, interest and additional charges quickly mount up.

As a rule of thumb, January 21 - this Thursday - is effectively the latest date to register with HMRC for the 2014/15 tax year, although the tax authority does not specify this date.

“Remember it can take at least seven working days - longer if you live abroad - to get the necessary activation codes,” said Rebecca Combes, partner and head of corporate tax at the South Coast office of Smith & Williamson, the accountancy, investment management and tax group.

She added: “Bear in mind that HMRC can issue penalties to taxpayers who miss the filing deadline because the necessary details do not reach them in time.”

Rebecca also warned taxpayers to be alert to online fraudsters who send ‘phishing’ emails.

“At this time of year there’s a spike in phishing emails which appear to come from HMRC. In fact, it has closed more than 22,000 fake websites in the last 18 months or so, which is an average of 40 websites per day. It’s a very real threat.

“So, if you are using HMRC’s free software, go to gov.uk to find the right place to file your return. HMRC says it will never send an email with a link to the software - so do not click on links in phishing emails that appear to come from HMRC.

"It’s also wise to change your government gateway password regularly as this reduces the chance of anyone else using it and stealing from your account by fraudulently amending your return online and rerouting a tax repayment.”

Rebecca also explained that completing a tax return can bring rewards.

“An estimated 180,000 higher-rate taxpayers making pension contributions forget to claim the full tax relief, leaving over £200 million in unclaimed relief. Even if you are enrolled in your employer’s money purchase group pension plan – one of the commonest arrangements – you may still need to claim the higher rate relief yourself.

“If a 40 per cent taxpayer puts an extra £800 into their pension, they are usually eligible for a total of £400 tax relief. While they automatically get tax relief of £200, making this a £1,000 gross payment into the scheme, the majority of people must claim the balance of £200 tax relief. To do this, they typically need to complete a self-assessment tax return.

“Finally, don’t miss the deadline just because you think you have no extra tax to pay. Even if your tax liability is nil but HMRC has asked you to file a return, you are likely to get a £100 fine if you miss the end of January filing date.

"However, HMRC has the power to cancel notices to file a return, so if you think you no longer need to submit one then do get in touch with HMRC – and the sooner the better.”

Rebecca’s top tips for completing the annual self-assessment tax return: 1. If you do not already have an online account, register straight away for online filing gov.uk/log-in-file-self-assessment-tax-return. 2. Collect the paperwork, which typically includes: a. For the employed: you need and year-end form (P60) and leaver form P45 from any employers you had in the year (or if those are lost you can use your final payslip for the year from your employer(s)) plus details of benefits in kind (P11D).

b. If you have investments: details of share dividends, sales, losses, interest on bank accounts and any other investments.

c. Rental property: details of incoming receipts, expenses, capital gains and losses.

d. Pension contributions: get confirmation of the amount you have contributed.

e. Details of any payments under gift aid to charities – higher rate taxpayers can claim the higher rate relief on this.

f. For the High Income Child Benefit Charge (HICBC): details of the child benefit received and knowledge of which partner has the higher income if over £50,000.

3. If you are missing some of the figures, make an estimate and explain your working.

4. If you anticipate a drop in your self-assessment taxable earnings for the 2015/16 tax year, you can claim a reduction in your payment on account.

5. Keep a record of your completed form and associated paperwork. If you are in a business, eg you are self-employed, keep this for a further five years (January 31, 2021) Otherwise, you must keep the paperwork until January 31, 2017.

6. Watch out for recent changes in the law which affect 2014/15 tax returns: a. If you have been moving in and out of the UK ensure you are aware of the statutory residence test rules.

b. If you have carried out any tax planning that might be deemed abusive, you may need advice.

7. If you are not sure about something, get help. This may be available from: a. Specialist tax advisers and accountants.

b. Voluntary organisations that deal with those on low incomes.

c. HMRC itself – although you can no longer visit an enquiry centre you can join an HMRC online chat session – details are on gov.uk