Charities will not lose out when the new lower rate of income tax is introduced next month, the Chancellor promised.

The voluntary sector had warned they could lose more than £90m a year when the basic rate of income tax falls from 22% to 20% next month.

But Alistair Darling's announcement included provision for Gift Aid, which enables charities to reclaim the tax paid on one-off donations, to be paid at a transitional rate of 22% for three years, meaning the level of benefit will remain the same.

The Charities Aid Foundation (CAF) had said the fall in the basic rate would reduce the amount of gift aid charities can claim on donations and had been urging people who plan to give a lump sum to charity to do so before the start of the new tax year.

Presently, once Gift Aid is included, every pound donated to charity is actually worth £1.28 to the charity in question.

But from April 5, when the basic rate falls from 22% to 20%, it would mean a drop to £1.25 for every pound donated.

Mr Darling said that introducing the transitional rate meant charities would receive extra Gift Aid worth about £300m between 2008 and 2011.

The Charities Aid Foundation said the Chancellor's announcement was "fantastic news" for charities.

John Low, the foundation's chief executive, said: "It is a huge relief. This will give charities a chance to adjust to the new lower rate."

He went on: "We will continue to discuss with government how best to promote and simplify Gift Aid and other forms of tax effective giving."

Labour MP David Blunkett, chairman of his party's manifesto group on the third sector, also welcomed Mr Darling's announcement.

He said: "This Budget ensures that many more of the organisations doing critically important work in our communities can benefit from the vital revenue that Gift Aid generates."

Oxfam estimated it would have lost at least £2m a year from the introduction of the lower basic income tax rate.

Phil Bloomer, the charity's campaigns and policy director, said: "We are very pleased that we do not have to budget for this significant loss for three years - by which time we hope the government will have introduced a better and simpler scheme to allow charities to benefit from Gift Aid."

Cabinet Office Minister Ed Miliband said the extra money to help charities - found by the Government in a "difficult fiscal climate" - would make British society "fairer and more just".