The UK's tax gap estimate rose to a record to £39.8 billion in 2022/23 as small businesses accounted for almost two thirds of unpaid tax, according to HMRC's data.
The tax gap was 4.8%, which is the difference between the amount of tax that should be paid to HMRC and what is actually paid.
The tax gap estimate for corporation tax for small businesses rose to £10.9 billion, while the tax gap for total corporation tax was £13.7 billion.
John Barnett, Chair of the Chartered Institute of Taxation's Technical Policy and Oversight Committee, said:
'Critics of HMRC can point to a record amount – nearly £40 billion – not being collected, but HMRC can legitimately point out that they are bringing in a record share of the expected tax take.
'That both these things can be true simultaneously tells us more about current tax levels than anything else.
'These figures show there is plenty of work for HMRC to do in a range of areas to reduce the tax gap. However, we should not lose sight of the fact that their record, collecting more than 95% of tax due, compares well internationally.'
Internet links: GOV.UK Chartered Institute of Taxation