Before you start off, read the whole form thoroughly and gather together all the paperwork you will need for the form (see box). It may look daunting but as long as you have the right information it is perfectly possible to fill in the forms without calling in professional help.
Call the Revenue helpline with your queries - it's open at weekends. The operators won't fill in the form for you, but they are helpful.
In the rest of this article we'll concentrate on some of the most common pitfalls:
Don't wait for paperwork: many taxpayers still do not realise that phrases like "as per P60" are not acceptable to the Inland Revenue. At the very least you should estimate the figure on the basis of information you do have, and indicate on the return that it is provisional and will be updated when the actual figure becomes available.
The Revenue is happy to get tax returns with estimates (as long as you supply actual figures when available), so don't miss the 30 September deadline just because you are waiting for the exact amount of interest you got on a savings account. If you do use an estimate, tick box 22.3 and explain in the white space for extra information why the full information is not available, and when it's expected.
Send as much information as possible: if you are self-employed it is often worth sending accounts and computations with the return where they contain extra information the tax office may need to understand the figures. This will ensure full disclosure to the Revenue. It is still essential to complete the boxes on the return (and the supplementary pages as appropriate) with the figures from the accounts or computations.
Take care on tax overpayments: One particularly confusing section of the form is question 19 which says "do you want to claim a repayment if you have paid too much tax?"
An attractive prospect, but many people last year answered "no" as they owed tax for 1995-96 or earlier years. Unfortunately those years are handled by a different computer system, and the effect is that any overpayment will be treated as a payment of tax in advance. It may be better to tick the "yes" box and note in the "additional information" box any repayment should be set off against any earlier years' liabilities.
Check personal allowances: Another area which has caught many people out is question 16 on allowances. It refers to the additional personal allowance available in some circumstances if you have a child living with you. Many married couples with children have claimed both the married couples' allowance and the extra personal allowance for children. In fact, this is only available to one-parent families, or to a married couple where one partner is disabled. The 1998-99 return does contain an extra box (16A) to try to make this clearer, but it is still causing problems.
Most returns rejected by the Revenue are sent back for very basic reasons. Apart from simple arithmetical errors, last time many people ticked the box, indicating that a supplementary page was attached, then forgot to include it.
The most common mistake in submitting a tax form is also the one easiest to sort out - forgetting to sign or date the return before sending it off.
Inland Revenue Self-Assessment Helpline: 0645 000444. The Inland Revenue website, www.inlandrevenue.gov.uk/home.htm has some useful hints, copy of the tax return and schedules to print off, as well as a self-assessment software package Tax Return Software (EVR). But you should note that the software package will only work for basic cases and cannot deal with self-employed individuals, share options, etc.
Anne Redston is a chartered tax adviser with Ernst & Young.
GET READY TO FILL IN YOUR TAX RETURN
Make sure you have the right forms to hand before you start. Sort paperwork this weekend: then you will have time to find any missing items well before 30 September deadline.
Make sure you have been sent the correct pages. As well as the main form, you may be sent supplementary pages for different areas of income (such as self-employment). Read through the notes with your return and see whether you should have been sent extra pages. Call the helpline to request extras.
Have a copy of last year's completed return: always copy each year's forms. If you haven't done it before, start now.
P60: all employees get one after the end of the tax year. It shows your pay in 1998-99.
P11D: you will have one of these forms if you get a taxable benefit from your employer, such as a car or health insurance.
Interest certificates from your bank or building society savings accounts.
You also need: share dividend vouchers; accounts (if self-employed); freelance earnings invoices; pensions books and statements; expenses records: anything you can set against earnings to cut the tax bill: include heating bills, cost of professional organisations and vocational training fees.