A campaign has been launched to encourage all savers on low incomes to check whether they are entitled to claim back tax.
Banks and building societies automatically take off the lower rate of 20 per cent tax from interest before it pays to savers, unless those who are not due to pay tax tell them not to.
The Inland Revenue estimates up to four million savers are set to gain. It has already contacted more than 21,000 pensioners on low incomes and paid back more than £7.3m in taxes.
Paymaster General Dawn Primarolo said: “Up to £300m could be waiting to be claimed, so it is vital that anyone who thinks they might be eligible contacts the Inland Revenue to find out more.”
Savers who are likely to qualify for tax back include children, students, part-time workers, people out of work and pensioners.
If savers claim by 31 January 2005, they can go back as far as 1998-1999 to get tax back.