The government has defended Budget plans to end age-related tax allowances for pensioners, amid claims they amount to a "raid" on their incomes.
It will lead to 4.4m pensioners being an average £83 a year worse off than they would have been, HMRC says.
But Chancellor George Osborne told the BBC no pensioner would be worse off in cash terms, and said state pension increases would leave them better off.
Labour said it was a hidden tax rise which would affect millions.
The change to pensioners' tax allowances dominates the newspaper coverage of Wednesday Budget speech - where it is widely described as a "granny tax".
Mr Osborne said his job in the Budget was not to write newspaper headlines, but to "get the British economy moving forward" - and pointed to an announcement by GlaxoSmithKline on Thursday that it was to invest £500m in manufacturing in the UK.
He denied that pensioners were being hit to pay for a tax cut for the very rich.
Prime Minister David Cameron said pensioners would receive the biggest ever increase in the state pension this April, adding: "It's a good Budget for our economy and it's a fair Budget for all our people."
The 50p tax rate for earnings over £150,000 was cut to 45p in the Budget from next year - at an estimated cost of £100m a year to the Exchequer - but Mr Osborne said other measures introduced would raise five times as much from those top earners.
He argued that the 50p rate was a "tax con" which did not raise enough money to justify the "enormous damage" it was doing to the economy. He said the richest 10% were paying the most under the government's deficit reduction plan.
Mr Osborne announced the age-related allowances freeze at the same time as revising the threshold below which under-65s pay no tax on their income - which he described as the "biggest tax cut for a generation".
That threshold will increase by £1,100 to £9,205 from April 2013 - a move the government says will benefit 23.6 million people.
Most basic rate taxpayers will gain £170 a year after inflation, while most higher rate taxpayers will benefit by £42.50 because the point at which most people start paying the higher rate is to be reduced from £42,475 to £41,450.
But the over-65s already get a tax allowance of £10,500 up to age 74 and £10,660 after that. From 5 April 2013, those allowances - which only benefit pensioners with an income below £29,000 - will be frozen and anyone turning 65 after that date will no longer qualify for the relief. The move will save £1bn a year by 2015.
The chancellor told the BBC that, with the personal tax allowance being raised "rapidly", it would have eventually overtaken the over-65s allowance anyway.
"It creates a much simpler system for everyone. I'm not embarrassed to say that pensioners are going to get the largest increase in the state pension from next month," he said, adding that the coalition had also guaranteed that state pensions went up in line with average earnings, prices or 2.5% - whichever is the greater.
"The net changes made by this government, including introducing this triple lock, mean that pensioners are better off."
Budget documents show that, taking inflation into account, this will leave 4.41 million people worse off, by an average of £83 a year in 2013-14. People due to turn 65 after 5 April 2013 could lose up to £322 annually.
And shadow chancellor Ed Balls told the BBC the big state pension rise was because inflation had been so high and it would not leave them better off.
"What [George Osborne] is doing is not putting the personal allowance up in line with inflation, so pensioners will actually pay more tax and people who are about to be pensioners are going to lose that allowance. Pensioners are worse off as a result of this Budget, it's a huge surprise."
He added: "The cumulative effect is to hit pensioners now, a big tax rise, families on £20,000 worse off, families on working tax credit on £17,000 massively worse off and the chancellor's decided his priority to make our economy stronger is to have one tax cut - a huge tax cut - for people above £150,000.
"I think in the country people will say: How can that be the priority how can that be fair how can than be right?"
'Relatively modest increase'
Groups representing pensioners said the measure was not fair while former Conservative Party chairman Lord Tebbit said the move was an "error" and "lousy politics".
"Unfortunately George Osborne, partly perhaps because of the unmannerly squabbling within the coalition, seems to me to have.... hurt a vulnerable group of the elderly," he wrote in hisDaily Telegraph blog.
"It hurts those who have saved enough for modest pensions. And if anyone does not know that most things become much more expensive as one gets older, then they will in the fullness of time."
The move will only affect over-65s earning more than £10,500. Those earning up to £25,400 currently receive the full age-related allowance but it is reduced in stages on earnings up to £100,000.
Ministers want to move towards a single tax allowance for those of working age and the retired, having set a goal of raising tax allowances for under-65s to £10,000 by 2015.
Paul Johnson, head of the Institute for Fiscal Studies, said poor and well-off pensioners would not be affected. Those that would lose out most were those about to turn 65 - but with a higher personal allowance for everyone, the amount lost was "much reduced".
"Despite this morning's headlines, this looks like a relatively modest tax increase on a group hitherto well sheltered from tax and benefit changes. From this Budget we calculate that pensioners will lose on average about one quarter of 1% of their income in 2014."
However he said Mr Osborne "should have avoided dressing up what is clearly a tax increase as merely a simplification".
The Institute for Public Policy Research also backed the move, arguing that younger people were facing record unemployment and cuts to benefits like education maintenance allowance, and it was "time for older people to share some of the burden of deficit reduction".