The UK's top tax man has refused to apologise after taking the wrong amount of tax from six million people.
Dave Hartnett, Permanent Secretary at Her Majesty's Revenue and Customs (HMRC), claimed media stories of blunders and IT failures were wrong.
He warned those owing £2,000 or more it must be repaid. Once a self-assessment form was issued they would have just over three months to pay in full.
Conservative MP Ian Liddell-Grainger accused HMRC of "built-in arrogance".
Speaking exclusively to Radio 4's Money Box programme, Mr Hartnett said: "I'm not sure I see a need to apologise."
He added: "I've read the papers, listened to the media and heard stories of HMRC blunders and IT failure - neither of those are true."
Mr Hartnett said the 5.7 million letters that he would be sending out to taxpayers before Christmas were the result of a normal process of matching the tax deducted from each taxpayer with their circumstances.
He confirmed that 1.4 million people would be told they had extra tax to pay.
And he revealed that those who owed the most tax would have the least time to pay.
"Those [who owe] more than £2,000… will be given an opportunity to pay based on a notice from us, or, failing that, they will be brought within self-assessment.
"People who enter self-assessment are expected to pay within three months and a little bit more."
Those owing below £2,000 will have the money deducted from their pay or pension over 12 months, or three years in cases of hardship.
Mr Hartnett said that system would apply to "more than 80%" of those who owed money.
But he defended the tighter deadline for the biggest bills.
"I think owing the most may actually mean they're earning the most… I think it's very unlikely that a low earner will owe us more than £2,000 as a result of the process we're going through."
An HMRC spokesman added that help was available to all people ordered to pay back tax, including those owing more than £2,000. Payments could be spread over a longer period with HMRC agreement, but interest would still be due on the outstanding balance.
The government has also raised the level at which any under payments will be disregarded from £50 to £300, meaning 900,000 people due to pay extra tax will not have to.
But Mr Liddell-Grainger MP, chairman of the All Party Parliamentary Taxation Group, said of HMRC: "They're one of these organisations that's grown and grown. They aren't actually up to it.
"You get this built-in arrogance we're hearing, where 'I don't need to apologise because I've not done anything wrong'."
John Andrews, chairman of the Low Incomes Tax Reform Group, said: "The £2,000 procedure gives me concern.
"There are circumstances in which over a two year period, for example on a bereavement where a widow suddenly inherits part of her late husband's pension, it is quite easy to run up this amount.
"I hope that HMRC would live up to the Your Charter expectations and look at individuals."
Mr Hartnett said that the main batches of letters to taxpayers would start going out in "early to mid October' and he still intended they would all arrive by Christmas.
Three quarters of those written to - 4.3 million people - will get a rebate averaging £400.
The rest, 1.4 million, will be told they have to pay the extra tax.
None will have to pay less than £300 and the average will be £1,428. Up to 250,000 could be asked for £2,000 or more.
BBC Radio 4's Money Box is broadcast on Saturdays at 1200 BST, and repeated on Sundays at 2100 BST.
BBC News website readers have been sending their reaction to the story.
This must be the most arrogant statement I have heard in years. Typical of the autocratic attitude taken by HMRC. I have not received a letter about my tax payment, but I am infuriated by Mr Hartnett's autocratic and arrogant attitude. Has he forgotten that he is first and foremost a servant of the British public. In private industry he would be forced to resign for such blunders. Joe Azzopardi, Skipton
Mr Hartnett's arrogance beggars belief. I remember watching him in an interview about tax office mistakes, and his attitude was exactly the same then: "we are a big organisation and we make mistakes - so what". John, Bristol
I can't quite remember what comes before a fall. Perhaps Mr Hartnett will remind me in due course. Ben, Dorset
I have to say that Mr Hartnett's comment that no apology is required seems somewhat arrogant to me. It cannot be disputed that "all is not well in the state of the HMRC". The response time to enquiries is now in excess of two months. My daughter wrote to her tax office in June because a bank had decided to change the way it dealt with tax on interest paid to her on a bond and that she owed HMRC some tax for last year. She is still waiting for a response along with thousands of others who are feeling quite exasperated about the Revenue's poor standard of administration. Philip Cooke, Birmingham
Regardless of how the error came to be made, the result has been confusion and expense, both for the taxpayers and HMRC. To say that no apology was required smacks more of stupidity than arrogance. Most people will apologise if they walk into someone. It's the sign of a weak character not to apologise. David Blake, London
I have been reading this story all week but not once has anybody, including HMRC, said how the error has happened. Now the big chief has said it is not an HMRC blunder, nor an IT failure, but has failed to give a satisfactory explanation. So exactly how did it happen? I am an ex-employee of HMRC and I can't see how it has affected only part of the population. Caroline, Pontypridd
Yes, HMRC should apologise - it is HMRC who calculate our taxes and who deduct them from our wages, so if a mistake has been made who is to blame? Rick Appleton, Rushall, West Midlands
I find it amazing that when a government department becomes more efficient in an effort to close the tax gap politicians try to lay blame on the brow beaten civil service. Isn't the country a bit strapped for the cash genuinely owed by taxpayers? In these times of austerity should we all not be paying our fair share as quickly as possible? Or this government will have to make even more severe public service cuts. Ray, Staffordshire
So taxpayers are to be punished for a fault that is not of their own making. Surely contrary to normal law? V M Alsford, Northampton