Customers with “queries that can be quickly and easily resolved online” will be directed to use HMRC’s online services from 11 December until the SA deadline on 31 January 2024.

Angela MacDonald, HMRC’s deputy chief executive and second permanent secretary, said: “The vast majority of self assessment customers file their returns digitally, so we’re helping them make the next step to resolving simpler queries through our online services.”

However, the Chartered Institute of Taxation (CIOT) said reductions to HMRC’s phone services were “misguided”.

John Barnett, chair of CIOT’s technical policy and oversight committee, said: “While we understand HMRC’s desire to prioritise where it puts its limited resources, we are concerned that in practice many of their customers will be unable to navigate HMRC’s digital services, and will simply give up.

“Previous trials to limit calls to complex queries, or diverting people to online services, have proven either troublesome or inconclusive. There is a significant risk of increased non-compliance, resulting in more penalties and subsequent appeals, creating more work for HMRC and taxpayers in the long run.”

CIOT is also concerned about the impact on agents during the self-assessment peak.

Mr Barnett said: “Many agents will be working flat out over the next eight weeks to ensure that their clients meet their self-assessment obligations by 31 January, working evenings and weekends in order to do so. Reducing access to HMRC support during this critical period does nothing to reassure agents that their efforts are appreciated.”

In a recent CIOT member survey, 89% of respondents said the cause for their contact couldn’t have been resolved online, yet 80% would use HMRC’s online services if they would resolve the issue.

Mr Barnett added: “Agents tell us that they normally only phone HMRC when they can’t resolve the issue online, and that if online functionality was available they would use it.

“There appears be a significant gulf between what HMRC believe agents can do online, and what agents themselves believe, and that should have been resolved before such a drastic change during such a busy period.”