HM Revenue and Customs (HMRC) provides phone numbers for taxpayers to ring for information, help and advice. But one-quarter of all calls to the 0845 number go unanswered and officials have no guidelines for how long a caller should expect to wait before someone picks up.

Exchequer Secretary David Gauke said: "HMRC does not have a target time for answering calls. HMRC uses a variety of measures to assess the accessibility of telephone services, which include the percentage of call attempts handled by its contact centres. In 2011/12, HMRC has improved the number of calls handled to 74% [compared with the 48% in the previous year]."