HMRC is experiencing huge delays in processing requests for unique taxpayer reference (UTR) codes, according to a report.
Some 407,510 startups were created during the 2020/21 tax year, despite the challenges presented by the COVID-19 pandemic.
Those who are unincorporated require a UTR code in order to file their first tax returns via self-assessment for the 2020/21 tax year.
The deadline to register for self-assessment was on 5 October 2021, with the tax office usually sending out codes out in the post within 10 days.
However, The Times reports that taxpayers who are going through self-assessment for the first time are in a "black hole of frustration".
One taxpayer said they applied for a UTR code on 20 August 2020 and still hadn't heard anything back from HMRC by 30 September 2021.
That individual described the tax authority's service as "horrendous so far", all while they were paying emergency tax at 30%.
Another taxpayer said they also applied for their UTR code in August 2020, and were told to expect it by February 2022.
The deadline to file tax returns for the 2020/21 tax year is on or before midnight on 31 January 2022.
Taxpayers who have not received their UTR code by that point will not incur an instant £100 late-filing penalty for missing that deadline.
Instead, they will have three months to submit their tax returns from the date their self-assessment record is set up.
Payment of any tax due should still be made by 31 January 2022 to avoid interest charges, and by 2 March 2022 to avoid a 5% late-payment penalty.
It's possible to do this without a UTR number as reference, by using a National Insurance number.
We can handle your tax return.