Plans to close 281 tax inquiry centres risk worsening an already "disgraceful" phone help service, a spending watchdog warned.
HM Revenue and Customs (HMRC) has been condemned for costing callers £136 million a year through delays in answering calls, with a quarter of 79 million calls unanswered - despite spending £900 million on customer service.
The Commons public accounts committee welcomed planned improvements, including a call-back system and a move away from expensive 0845 numbers.
But it condemned a "woefully inadequate and unambitious" new target to answer 80% of calls within five minutes which is said was way below industry standards.
And it said there was a "real risk" of things actually getting worse with new tax and benefit systems likely to add to the volume of calls while staff numbers were being cut.