Taxpayers have to wait almost three times longer to contact HM Revenue & Customs than they did two years ago, it has been revealed.
On average it takes just over four minutes to get through to an adviser on the phone, compared to one minute and 31 seconds in 2010.
Shadow Treasury minister Owen Smith, who obtained the figures by tabling parliamentary questions, says they show "chaos and incompetence" in the system.
HMRC's helpline is automatically answered within a few rings but callers are then given a range of options and often spend time on hold.
One in four people apparently hangs up before being connected to an adviser.
Call waiting times nearly trebled
Smith says: "With average call waiting times almost trebling in the last two years, this is yet more evidence of chaos and incompetence in government.
"Families with children are facing massive cuts to tax credits and are set to lose an average of £511 a year as a result of the unfair policies of this out of touch Tory-led Government.
"So it's outrageous that they are waiting longer and often struggling to get through for much needed information and advice.
"These costly delays are also unacceptable for families, pensioners and businesses trying to give HMRC information to ensure they are paying the right amount of tax or getting the correct level of tax credits.
"With the economy now back in recession because of David Cameron and George Osborne's economic mistakes and complicated changes to child benefit just a few months away, ministers urgently need to get a grip."
HMRC 'working hard to improve'
A HMRC spokeswoman says the department handles 60 million calls a year.
"During busy periods, there will be times when customers find it more difficult to get through," she says.
"We are working hard to improve contact centre service levels and have made good progress.
"We are managing busy periods better by deploying extra people to deal with short-term increases in demand."