The clock is ticking for the estimated two million taxpayers who have yet to meet the January 31 deadline for handing in their self-assessment forms for the year 2006-07. There are only five days left until the cut-off point at midnight on Thursday, by which time tax returns must have reached the Revenue, along with any money due.

The customary last-minute scramble could be made even more chaotic this year by the possibility of a strike by civil servants on January 31, which may result in the closure of some tax offices. In addition, some taxpayers whose homes have been blighted by last year’s floods may have lost their financial records.

The Revenue has promised to do everything possible to keep offices open before and on deadline day and to assist those who have lost vital records. But Revenue officials and accountants urge all those who are required to file returns not to leave it until the last minute.

Late returns trigger an automatic £100 fine. For persistent offenders there is also the possibility of £60-a-day penalties until the form is handed in. Any overdue tax incurs interest of 7.5 per cent a year and there will be a further one-off charge of 5 per cent on any money that is still unpaid by February 28.

Taxpayers have the choice of filling in a form or filing online. Last year nearly three million of the nine million individuals required to complete self-assessment returns filed online.

So with time running out, Times Money offers a checklist to help you to beat the deadline.

DO check that you actually need to complete a tax return. If in doubt, ask the Revenue, which also publishes a useful summary of who does and does not need to file on its website at www.hmrc.gov.uk.

DO make certain that you have all the pages you need to complete your return. For example, you will require supplementary pages if you receive income from letting property. You can obtain these from the self-assess-ment orderline on 0845 9000404, or download them from the website.

DO make sure that you have all the information you need before sitting down to complete the form. This will include things such as your P60, if you are an employee, and your P11D, if you receive taxable benefits or expenses. You will also need details of savings interest and dividend payments, plus accounts if you run your own business. If you have paperwork missing, give estimated figures and explain what you have done.

DO remember that the Revenue can be your friend, rather than your enemy. Each local tax office has a self-assessment team that you can ring for help. When the office is closed, you can call the self-assess-ment helpline on 0845 9000444. It is open evenings and weekends.

DO double-check your form for errors. Anita Monteith, of the Institute of Chartered Accountants in England and Wales (ICAEW), says: “A form that is not completed correctly can be rejected by the Revenue so it is important to check everything.”

DO compare this year’s return with the previous year’s form. If there are any significant changes, it is worth offering a brief explanation in the space at the end of the form – it could save you from an investigation by the Revenue.

DON’T send any papers with the tax return. However, you do need to keep records of information used to complete tax returns. In most cases they should be kept for 22 months after the end of the relevant tax year, though this is extended to five years and ten months for those running a business or who have income from letting property.

DON’T forget to sign and date the form and make sure that you fill in all the boxes that apply to you. If you owe money, make sure you have included a cheque for the tax due.

DON’T leave things until the last minute. It may take longer than you think to complete the form.

DON’T try to file online if you do not already have a user ID and password from the Revenue. Leonie Kerswill, of PricewaterhouseCoopers, the accountant, says: “They take a week to obtain, by which time the deadline will have passed.”

DO keep a photocopy of your completed form. Mrs Monteith says: “Sometimes forms get lost and you do not want to have to do everything all over again. If you use the online filing service, keep a note of the details you have entered.”

Who needs to self-assess

About nine million people are required to fill in a self-assessment tax form each year. This number has been cut by about 1.5 million in recent years thanks to a streamlining process that has removed various categories of taxpayer from the list.

Those who have been released from having to file a return every year include pensioners with extra investment income that the Revenue regards as fairly straightforward and employed people who take on freelance work in some years but not in others.

However, the onus is on all taxpayers to keep the Revenue informed of all their earnings each year. If in doubt, call the self-assessment helpline on 0845 9000444. Those who must fill in a self-assessment form include the following groups of people:

Those who work for themselves, either self-employed or in a partnership; Company directors; Lloyd’s of London names or members; Ministers of religion;

Those who receive income from letting a property or land; Those who receive income; annually from a trust or settlement; Those with taxable foreign income; Those who receive other untaxed income that cannot be collected through PAYE.

Even if you do not fall into these categories, you will need to fill in a tax return if you have annual income from savings or investments of £10,000 or more before tax, or if you have annual income of £100,000 or more.

Get it right first time

Failing to complete your tax return accurately could cost you both time and money. You may be asked to file it again, and if you underestimate your tax liability, you will have to pay it later, with the possibility of penalties for overdue tax thrown in.

The Revenue has compiled a list of the most common reasons for tax returns to be corrected, of which taxpayers should take heed when completing the forms.

The most common errors made on self-assessment forms

Failure to complete a separate supplementary page for each individual employment.

Entering the net figure of employee personal pension premiums instead of the gross figure (ie, claiming insufficient relief where higher rates of tax are payable).

Entering the figure for capital expenditure allowances in Box 3.14 of the self-employment pages instead of the figure for capital allowances.

Failure to complete question 19 of the main tax return where a repayment is due. If you do not opt for immediate repayment, the Revenue wil leave the overpaid amount on your account and set that amount against future liabilities.

Entering your pay in box 1.8 of the employment pages but not entering tax deducted in box 1.11.

The most common reasons for rejecting a tax return

Entering a “yes” tick on one of the questions 1 to 9 on page 2 of the tax return but failing to forward the relevant supplementary page. expenses. You will also need details of savings interest and dividend payments, plus accounts if you run your own business. If you have paperwork missing, give estimated figures and explain what you have done.

Failure to complete the self-employment pages, particularly from box 3.74 onwards.

Putting detailed information on separate schedules instead of including the information on the self-assessment tax return.

Entering handwritten notes on the self-assessment form, such as “per accounts” or “information to follow”, instead of entering actual figures on the tax return.

Failure to sign and date the self-assessment tax return.

For further information, visit the Revenue website at www.hmrc.gov.uk. Alternatively, you can call the dedicated self-assessment helpline on 0845 9000444.

CASE STUDY: Step-by-step software makes sense of the jargon

Hilary Belden, of Putney, southwest London, works as an education project manager for Ealing council and has a number of investments in stocks and shares and unit trusts, as well as a property in Herefordshire, which she has rented out from time to time.

To help with her annual self-assessment tax return, Ms Belden, 60, has made use of TaxCalc, a software programme that takes her through the various sections one by one. She says: “I have used TaxCalc for several years and found it really helpful. The best part is the step-by-step guide because it really simplifies things. The Revenue form uses so much jargon that it can be extremely confusing.

“I also give away some of my income to my church and to various charities. The TaxCalc software is very good at working out the tax implications of this.”