Taxpayers are being urged not to overlook a looming payment deadline owing to summer holidays, otherwise they face a fine.
Nearly five million self-employed people, company directors and those with more than one source of income may have to pay tax by 31 July.
The major filing deadline for those in the self-assessment system is 31 January.
However, those who make payments on account face a deadline on Monday.
Paul Haywood-Schiefer, of accountants Blick Rothenberg, said: “Individuals completing annual tax returns within the self-assessment regime and making payments on account should be making a payment.
“Typically self-employed traders, those with rental income and those with large amounts of investment income are included in this group, which paid over £6.6bn to the Revenue in July last year.”
Payments on account are based on the previous tax year’s income tax liability, assuming that this will not change.
Chas Roy-Chowdhury, head of taxation at the accountancy association, the ACCA, said that summer getaways often led to people forgetting about the deadline – but such a mistake could lead to a fine of 5% of the tax owed.
“Ignorance and naivety are no excuse when it comes to tax filing,” he said.
“Many holidaymakers have probably been more focused on exchange rates and how to afford those extra holiday treats.
“However, this [tax payment] is not something that can be left until you come back from your summer break, or even leaving it until the last minute and trying to do it yourself. The consequences of not paying on time or paying the wrong amount are high.”