Responding to a question from Fine Gael MEP Brian Hayes at the European Parliament's ECON Committee, Ms Vestager said the the tracker issue raised matters that the Commission takes "very seriously".

Mr Hayes asked the commissioner whether she believed Irish banks had acted as a cartel and whether the decisions by the banks to prevent thousands of customers from returning to their tracker rates after their fixed loan terms were an example of anti-competitive practice.

Ms Vestager said at first instance the Irish Competition and Consumer Protection Commission would look into any competition law issues and would act on any evidence that banks had acted in concert. No such evidence has been produced to date.

Ms Vestager said she would encourage any bank employees to come forward under whistleblower legislation either to the CCPC or to the EU Commission's Competition Directorate-General if they had concerns or wanted to make a confidential disclosure.

"I would invite anyone who has evidence when it comes to the competition side of this thing to come forward one way or another," she said.