Total tax debt hit £44.5bn in June - a 6% increase on the same time last year - according to the latest figures from HMRC.
While HMRC said there was "little change" in the proportion of customers filing their tax returns before the deadline, the number of customers paying on time has reduced, resulting in a higher volume of new debt.
Small businesses are increasingly failing to pay outstanding tax bills, with the average value of debt also rising.
According to the tax authority, these figures suggest that customers "remain committed" to complying with their tax obligations, but are "struggling to pay". It continued:
"Even though we are resolving debts at levels significantly above the average for tax years from April 2017 to March 2020, the volume of new debt exceeds the level at which we are able to resolve it."
HMRC advises people who are struggling to pay their tax bill to flag this as soon as possible and says support is available, such as its flexible time to pay arrangement, which can be set up online to collect tax debt in instalments.
By the end of 2022 to 2023, 912,000 users were using time to pay arrangements to pay off £5.7bn of tax debt - a 7.5% increase compared to the end of 2021 to 2022.
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