HMRC's move towards almost exclusive online filing resulted in 85.5% of returns being sent online, with the busiest days for filing coming on 30 and 31 January, when HMRC received 980,000 returns. The busiest hour was between 1pm and 2pm on 30 January, when almost 50,000 returns were received – 830 per minute.

The number of online returns was up by 2.4% this year, while HMRC is currently reviewing the level of outstanding Self Assessment returns, but performance was better than last year.

The busiest hour on the 31 January deadline day was between 11 am and midday, when almost 32,000 returns were received – 530 per minute. HMRC also answered 95% of calls first time on deadline day.

Around 4.3m customers (42%) left it until January to file their returns, which HMRC issued in April 2014.

By the end of January, more than a million Self Assessment-only customers (self-employed, with no other source of income, no employees and not VAT-registered) opted to receive electronic messages from HMRC, rather than paper communications.

HMRC’s director general of personal tax, Ruth Owen, said: ‘This is another record-breaking year for Self Assessment, with 210,000 more people filing their returns on time than last year.

‘We’re grateful to the overwhelming majority of people who sent their returns on time. If you’re one of the minority who missed the deadline, you still need to get your tax return to us as soon as possible, to avoid further penalties and interest mounting up.’

Missing the tax return deadline results in an automatic £100 late-filing penalty. There are further late-filing penalties after three, six and 12 months. People with a genuine reason for not filing should contact HMRC to ensure they do not incur more penalties.

For anyone who still hasn’t filed their return, go to www.gov.uk/self-assessment-tax-returns or the Self Assessment helpline on 0300 200 3310 (open 8am to 8pm, Monday to Friday, and 8am to 4pm on Saturday).