TAX staff have been moved from other duties to deal with a deluge of phone calls about new tax credits.
Millions of people have swamped the £53m national helpline with inquiries for the Working Tax Credit and Child Tax Credit.
Many callers have complained that they cannot get through and face long waits.
The Inland Revenue has drafted in 700 staff to join the 2,000 already working on the helpline at centres across the country, including one in Peterlee, County Durham.
A spokesman said: "The helpline has been in operation since September and, over the last week, it has got extremely busy because of the time of year. Last week, we started employing extra people to answer more phones.
"The additional staff will be able to deal with an extra 200,000 calls a week. Nine out of ten families are eligible for the new credit and we have had millions of applications."
The Working Tax Credit is for people who work at least 16 hours a week or are self-employed. The Child Tax Credit is to help families with childcare costs. So far, 3.9 million families have applied for the credits.
The helpline number is 0845 300 3900, or information is available at www.inlandrev enue.gov.uk
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