The self-assessment tax system will collapse if new filing dates for the self-employed are enforced, the Institute of Taxation has warned. It has rejected as unsatisfactory a proposal put forward by the Minister for Finance, Mr McCreevy, who has said he is willing to consult further with the industry before the new filing dates come into operation.

The recent Finance Bill included a provision under which the date by which the self-employed would file their tax returns moved from January 31st of the following year to November 30th.

This would mean, for example, that from the 1998/99 tax year, the taxpayer would make a final return in November 1999, instead of January 2000.

Following strong criticism of the move, Mr McCreevy said that the new measure, which was to apply from November 1999, would remain in the Bill, but would be subject to a commencement order from the Minister. This would allow time for consultation with tax professionals on the issue.

However, yesterday evening Mr Rory Meehan, chairman of the institute, said that leaving the new filing dates in the legislation would mean "the final result is known before the consultation has taken place".

Changing the filing date back to November would "lead to a collapse in the workings of the self-assessment system", he warned.

The institute had researched its members and received an unprecedented number of submissions and calls on this issue since the measure was announced in the Finance Bill.

"Four out of five of those surveyed stated that they believed the proposed changes would lead to an unworkable situation for themselves and their clients," according to the institute's statement.

"No other issue has caused such concern among tax practitioners in living memory," the statement added.

Tax practitioners are already under enormous pressure to comply with the January 31st filing date on behalf of their clients, according to the institute. This pressure would go beyond breaking point if a November 30th date was introduced.

The Minister said in the Dail this week that he believed there was a case for moving to a calendar year tax system and that this would be an issue worth discussing.

The existing system , where the tax year ended on April 5th, was based on old tradition, he said, and should be re-examined.