The European Commission has officially accused Ireland of negotiating two special tax deals with Apple.

In official documents published this morning, it says the Revenue Commissioners agreed special tax deals with the computer company in 1991 and 2007.

It claims that Ireland did not change its usual corporate tax rate - but instead negotiated with Apple to decide how much of its profits would be taxed within this country.

The document forms the basis for a full investigation by the Commission into Apple's tax affairs, which could take several years.

Apple could be forced to pay decades of tax in arrears if it is deemed to have received unfair state aid from the Irish government.

Ireland has always denied striking any special tax deals with multinational firms.

The government is insisting Apple did not receive selective treatment and was taxed fully in accordance with the law.

In a  statement yesterday, the Department of Finance reiterated that "Ireland is confident that there is no breach of State aid rules in this case."

The government said the document to be published by the Commission does not contain any ruling, but will rather set out that it is examining allegations.

The Department statement explains, "it is expected that a final decision in relation to this investigation will take a considerable period of time. The purpose of the publication of the Opening Decision is to give interested parties the opportunity to submit comments directly to the European Commission."

The Commission launched its investigation into the tax arrangements between Apple and the Irish government after US senate hearings last year highlighted that billions of dollars in profits were shifted out of the US to international subsidiaries.

The Department of Finance has previously said it is confident there was no State aid breach and that it will defend its position "vigorously".

The statement added, "We understand that the European Commission has a responsibility to investigate potential breaches of state aid rules, so we will continue to do everything we can to ensure that they have the full information they require".

Apple has said it "pays every euro of every tax that we owe. Since the iPhone launched in 2007, our taxes in Ireland have increased tenfold".