HM Revenue and Customs (HMRC) failed to answer 44 million phone calls last year, according to the National Audit Office (NAO).
Although it employs the equivalent of 10,500 full time staff at a cost of £233mn, it failed to answer 43% of calls received, and, during the tax credit renewals peak, just one in three calls were picked up
Those who did manage to get through were kept waiting for an average of two minutes, rising to four minutes at the busiest times, the NAO says.
By contrast, the best practice target in the private sector is for 90% of all calls to be picked up within 10 seconds.
Although the latest figures for the first half of 2009/10 have shown some improvement, the NAO says more than 27% of calls were still not getting a reply.
Despite attempts to encourage customers to use the Internet, calls to HMRC rose by 22% last year.
Perhaps even more worryingly, HMRC estimates 11 out of every 100 callers are given inaccurate advice.
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