HMRC has revealed that the average wait time for its self-assessment helpline is 27 minutes - more than double the same time last year.
In response to a letter from the Treasury earlier this month, HMRC denied that call centre staff working from home caused a decrease in productivity.
HMRC also encouraged self-assessment customers not to leave their returns to the last minute, saying that they have a "generous" ten months to do so.
The tax authority said that taxpayers should use its web services instead of phoning wherever possible, estimating that 65% of calls to the helpline could have been resolved online.
HMRC's digital assistant has handled around 105,000 interactions in December 2022 and January 2023 so far, providing the answer automatically in more than half of them.
According to HMRC chief executive Jim Harra, the satisfaction rate for customers using HMRC's webchat to speak to an advisor was 81%, which is above industry standard.
Commenting on the long wait times, Harra said:
"Despite our helplines being busy, all callers who need to speak to an adviser can do so, but they may have to wait longer than usual for their call to be picked up, or at exceptionally busy times, they may have to call back."
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