Question to the HM Treasury:

To ask the Chancellor of the Exchequer, how many complaints HM Revenue and Customs received in each of the last five years; and what proportion of those were upheld.

Monthly performance data is published on GOV.UK website.

Volumes of complaints received, and outcomes can be viewed in the supporting data tables found here:

https://www.gov.uk/government/collections/hmrc-monthly-performance-reports

HMRC monthly performance reports - GOV.UK (www.gov.uk)