HMRC has received 6.6m tax returns as of January 4, out of a total 12.1m returns due to be filed before the January 31 deadline.
The majority of these returns (93 per cent) have been submitted online, with only 450,000 returns filed on paper (7 per cent).
Almost 18,000 taxpayers filed their tax return on New Year’s Day.
Those who have yet to file are being urged to act now as it could take longer than originally expected.
Karl Khan, HMRC’s interim director general for customer services, said: “In what was a very difficult year for many, we are grateful to the 55 per cent of our customers who have already submitted their returns.
“HMRC is ready to offer support to those who are yet to file their returns or are worried about paying their tax bill, but they must act now so we can help before the deadline.”
Once individuals have completed their tax return, and know how much tax is owed, they can set up their own payment plan to help spread the cost of their tax liabilities, up to the value of £30,000.
But some in the industry are calling on the tax authority to extend the filing deadline by at least one month.
Robert Salter, a service director at tax and advisory firm Blick Rothenberg, said: “With the various lockdowns that people have experienced since March 2020, many are struggling to get together the data that they need - often from third parties.
“However, as things presently stand, if they are not able to finalise their tax returns by the 31st, they would be subject to automatic late filing penalties - even if there is no tax due."
He has called on the government to extend the deadline by at least four weeks but preferably even by as much as six or eight weeks.
Mr Salter said: “This will provide additional time for taxpayers to gather the data they need to file the tax return correctly, but also provides the following advantages.
"Extending the tax return filing deadline in this way will provide HMRC with more opportunity to actually issue tax return ID Numbers (Unique Taxpayer Reference Numbers), which are an essential requirement for tax returns to be filed electronically."
He added: “The government has actually already shown some flexibility with the self-assessment tax system - e.g, re payments on account and balancing tax liabilities.