How to amend previously submitted tax returns?

Ian Says

You can only include expenses for the tax year in question on that year's Return, subject to the pre-trading expenditure rules.

Your solution is simple - redo the Tax Return for the year in question and submit an error or mistake claim with the revised Tax Return for the year in question.

Be prepared for the Revenue to ask for backing details for the entries on your Return and they may open an enquiry into the Tax Return on the basis they suspect your record keeping is not up to scratch.

Dependent on the time frame it is open to the Revenue to accept or reject your claim as they see fit. If it is within the time limit for amendments to that year's Tax Return then there is no need to make the error or mistake claim, merely submit a revised Return and a letter saying why you are doing it.

If you are past the time limit for amendments, then the Revenue have the power to accept or reject the claim as they see fit.

Usually they will accept the claim on the basis of being 'fair' to taxpayers.