Taxpayers waited about four minutes to speak to an adviser at peak times
More than 40% of calls to HM Revenue and Customs last year were not answered despite a drive to get taxpayers to use the telephone, a report has found.
Of the 100 million calls to the main HMRC helplines from 2008 to 2009, 40 million did not get through, parliament's spending watchdog found.
The House of Commons Public Accounts Committee (PAC) condemned the taxman's call-handling operation as "poor".
Revenue and Customs said that, by next year, it aimed to answer 90% of calls.
The government will formally respond to the report in due course, it added.
However the Public Accounts Committee (PAC) report said Revenue and Customs needed to be "more ambitious" in improving its service to callers.
The department's target of answering 90% of calls would still fall short of the industry standard of 95%, it said. It also urged HMRC to answer all calls in less than a minute.
Last year customers with queries about their tax bills had to listen to a recorded voice for an average of two minutes before they were able to speak to an adviser.
At peak times, the average wait rose to four minutes, the report found.
HMRC contact centre staff spend 38% of their time handling calls, compared with an industry benchmark of 60%, it said.
The report also urged HMRC to reduce the confusion caused by running 139 separate telephone numbers and to avoid unnecessary calls by making its written material easier to understand.
Committee chairman Edward Leigh said: "If an organisation wants more of its customers to contact it by telephone, then it has got to be good at answering calls.
"HMRC unfortunately is not very good at answering calls, its performance remaining well below industry best practice standards.
"Staffing levels should be matched more closely to the peaks and troughs of demand and the department must do more to cut the number of calls it regards as unnecessary."
HMRC has been encouraging taxpayers to sort out queries over the phone or internet rather than letters and face-to-face interviews in order to save money.