The multimillion pound investment, which is part of the current spending settlement and not additional funding from the Treasury, covers the cost of paying for the recruitment of around 3,000 additional staff this year and for allocating around 2,000 staff from other HMRC business areas on a temporary basis to handle high call loads in the run-up to the tax credits deadline next month.

HMRC receives more than 60m calls a year, peaking around key deadlines such as 31 January for Self Assessment, and 31 July for tax credits renewals.