Dr Tom McCluskey, a lecturer at Dublin City University Business School, said unclaimed relief would cease to be a problem for the Revenue and PAYE workers if each taxpayer had to submit a return to reconcile their tax bill with their entitlements under the tax code, as in the US.

Tuesday is the deadline for Americans to file tax returns and the Internal Revenue Service in Washington will process 120 million returns.

Only about 5% of Irish taxpayers file a tax return each year.

"In contrast with the United States, where everyone has to file by a specific date, there is a degree of inertia here, " said McCluskey.

"The only way to cover this is to have everybody file and make it simple enough for everyone to file easily."

A draft report issued earlier in the month by the Oireachtas Joint Committee on Finance and the Public Service estimates taxpayers are owed up to Euro350m in unclaimed credits, reliefs and allowances. The report blames the Revenue for the failure of taxpayers to take full advantage of their entitlements and describes its efforts to communicate with its customers as"officious", "unintelligible" and "incomprehensible". It makes no reference, however, to legislative changes that could simplify the tax code or increase the number of tax returns.

McCluskey said it was difficult to blame the Revenue, since it only implements policy and has been making efforts to encourage people to claim their reliefs. Revenue spent nearly Euro700,000 on public awareness campaigns and distributed more than two million PAYE information leaflets in 2006.

A spokesman for the Revenue said tax officials would "prefer the simplest system possible" but that the current system is "complex and complicated".