A KEY deadline in the tax year is looming at the end of this month.

The nine million people who come under the umbrella of self-assessment should be filing their tax returns for last year by September 30.

If they do, the Inland Revenue will calculate their tax liability for the past year (1999-2000). If they don't meet the deadline, they will have to do the calculation themselves.

Since September 30 is a Saturday, they effectively have until September 29 to file the return.

The kind of people who come under the umbrella of self-assessment include the self-employed, higher rate taxpayers and company directors.

Filling in the return is quite a task in itself but, according to financial experts VirtuallyAnywhere.co.uk, it pales into insignificance beside the monumental task facing those who are obliged to complete the tax calculation as well.

A VirtuallyAnywhere spokesman said: "They will have to tackle a 29-page calculation, with more than 500 boxes to consider, a task bewildering for even experienced accountants."

So the message is: fill in the return and get it off before the deadline to avoid real complications later on.

Maurice Fitzpatrick, a partner at accountants Chantry Vellacott, said self-assessment taxpayers should tackle the process of form-filling in three separate stages.

He said: "First of all you need to gather together the various things you are going to need.

"These will include details of your pay and benefits from your employer or details of your accounts if you are self-employed.

"You will also need details of any bank interest, building society interest and dividends received, plus a copy of last year's tax return, which is useful as a guideline.

"The second step is to start filling in the form, including the various figures for income, capital gains and investment income.

"You also need to list your expenses, including pension contributions and expenses incurred in your employment.

"Thirdly you should do a recheck of your return, making sure you put everything in the form that you need to.

"Ask yourself whether your circumstances have changed in the tax year 1999-2000, as compared with 1998-99."

Anna Collins, head of tax at Towry Law, has a few additional hints to offer.

She said: "Everyone should read page two of the return to establish what, if any, supplementary pages they need to complete.

"The self-employed, those in employment or in receipt of rental income, for example, will need to complete the supplementary pages.

"These can be ordered from the Inland Revenue's order line if they were not sent with the original tax return."

She added that it would be necessary to gather all documents relating to income, gains and tax deducted for the year in question because it is necessary to disclose income even if tax has been deducted from it at source. Her other tips are:

:: Write clearly and make entries only in the boxes provided. Any entries on the pages themselves will not be read.

:: Use the additional information boxes for any relevant information but bear in mind these will not automatically be looked at by the Inland Revenue.

:: No-one should attach anything to the tax return. The Inland Revenue may not look at these when processing returns and the documents may not be returned.

:: People should enter only half of any joint sources of income unless they have made an election for another split.

:: Remember to sign and date the tax return.

:: Everyone should make an attempt to do a rough calculation of their tax liability so that they have some idea what to expect from the Inland Revenue's calculations

:: Where someone is claiming a repayment of tax they should ensure they tick the yes box at question 17 on page 7 of the return and fill in the appropriate boxes.

One item which is not on the self-assessment form is the possible entitlement to a tax refund if you are a company employee but work from home one or more days a week.

According to accountants at Instant Tax Refund, employees in this position can claim reimbursement for the additional cost of heating lighting and other expenditure whilst working at home on their employer's behalf.

A spokesman for Instant Tax Refund said: "Not many people know that and there is no mechanism at the moment for easily making this claim.

"It is not on the self-assessment form and the calculations are not published by the Inland Revenue."

POUNDNOTES

:: The Annuity Bureau has introduced a fast-track consumer response service to its web site. It ensures all e-mail enquiries sent to the site about things like annuities or income drawdown receive a reply within two hours.

:: Policy Portfolio, which deals in traded endowment policies, has launched a new web site where consumers wishing to sell their endowment policies can submit details online and receive a free valuation within 48 hours.

:: The Leeds & Holbeck is offering the chance to invest in a three-year FTSE Bond promising a return of 29.5% over the 36-month period provided the FTSE Index of leading shares rises during the three-year term. If it fails to achieve this people will get back their original investment.

:: Barclays is providing a new fee-free mortgage service. Homeowners switching their home loan to a Barclays Base Rate Tracker will have no legal, valuation or booking fees to pay.

:: Barclays Stockbrokers has launched a new Internet service called Portfolio Online. In addition to a special deal on stock switching, it offers real time portfolio valuations and real time prices as well as a special "price improver" quote.