The Revenue is placing posters and leaflets in all main post offices, telling people to ask for the rebates by calling a special freephone number. Freepost reply coupons are also available.
In the past two years about pounds 300m of tax has been repaid on bank and building society accounts. The last Taxback campaign ran over the first six months of last year.
Two million leaflets were handed out to pensioners and child benefit claimants at main post offices in the final week of June.
The campaign produced half a million responses and led to pounds 50m in repayments. More than 9 million people so far have registered to have no tax deducted from their interest, but several million more may be eligible.
An Inland Revenue spokeswoman said: 'We think that there is about pounds 600m unclaimed in 1991/92 and 1992/93. Because people are registering all the time, there will be less of them claiming in the future, and the annual amount of money to be claimed is likely to fall.
'But there appear to be some people who will not apply, no matter what campaign we run.
'It is hard to say why that is. Maybe they are still not aware of their entitlements, or perhaps they believe the amount is too small for them to bother.'
Post offices are being targeted, because they are where the Revenue expects to reach the greatest number of people on low incomes. People can either claim back their tax or they can register to receive their interest in full, with no tax deducted. Once registered, interest is paid gross until banks are told otherwise.
Freephone 0800 660800 for more information.
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