The online filing system came under fierce criticism this week, with advisers saying that it has not kept pace with changes introduced to the tax system.

The government has overhauled its guidance on various areas of tax, but new disclosure requirements have not been fully implemented online, leading to what advisers say is a larger number of returns being rejected.

HMRC introduced changes to simplify complex tax returns ­ for example, by ensuring those with partnership incomes under £30,000 have to fill in fewer boxes than previously. But software industry experts pointed out that while changes had been made in many areas, the online filing system had not kept pace.

The problems have dismayed tax software suppliers, which had warned there would be problems.

‘We warned HMRC a year ago that it needed rigorous testing before going live, but they didn’t listen to us,’ said former BASDA president Dennis Keeling.

Paul Aplin, chairman of the ICAEW tax faculty and tax partner at AC Mole & Sons, said that the ‘number of rejections were noticeably higher this year’, adding: ‘Someone has to get a handle on where the problem is quickly.’

Paul Onions, operating director for PTP Group, a division of Iris, said: ‘If you follow the guidance notes from HMRC when completing the returns it will be rejected.

‘Customers are contacting their software support lines for explanations for what are actually HMRC issues. We, like many software houses, have made changes to our programming to compensate for these HMRC errors.’

HMRC said it had been working with software vendors: 'There have been teething issues with implementation of the validation process. We are experiencing a higher validation failure than in previous years for some, but not all, commercially developed products. The position varies from product to product and some have achieved a 100% successful submission rate.

'Although the validation failure rate for some products is higher than in previous years, we have seen this fall steadily and we are now close to the rate experienced last year.'