The European Commission has ordered Ireland to recoup 13 billion euro from tech giant Apple over a sweetheart tax deal.

The decision follows a three-year investigation by the EU Competition Commissioner into the tech giant's structures and "back-room" deals dating back to 1991.

The basis of the case against Ireland and Apple was that the multinational secured a tax advantage which was not available to other companies.

In 2014, Brussels warned the Irish government it had concerns tax calculations amounted to a sweetheart deal by under-estimating taxable profit on Apple products like iPhones and iPads, creating an unfair advantage.

Both Apple and the Irish government, who have always denied breaching state aid rules, are likely to challenge the decision in the European courts.