The self-assessment tax return deadline has been pushed back by a day, HM Revenue & Customs has confirmed, after the online filing system went down on deadline day.

The deadline will now be 1 February at midnight rather than the original deadline of 31 January.

The department said the system would be up-and-running again shortly. It went down at around 10:30am on Thursday.

Advisers expressed frustration at the delay.

'It's completely unacceptable that a State-operated system catering for the entire population can't cope with an estimated 150,000 to 200,000 filings in one day, whereas large corporate IT systems regularly cope with volumes vastly in excess of this,' said Baker Tilly's head of tax George Bull.

Other IT systems at HMRC that enocuntered difficulties included included the electronic filing for the Construction Industry Scheme, Corporation Tax, PAYE, Pension Schemes and Stamp Taxes online.

Advisers believe that the IT problems lie with HMRC's systems as people using third-party IT systems had not encountered any problems.

The self-assessment system was back up at 3.30pm on Thursday and 104,000 people were able to file their returns, adding to the 3.6m returns filed online earlier.