It said the banks - Bank of Ireland, Allied Irish Banks, Educational Building Society (EBS), GE Money, Permanent TSB (PTSB) and Royal Bank of Scotland's Ulster Bank - have been ordered to review sales of the insurance product since August 2007.

Britain's banks have already set aside over 10 billion pounds ($16 billion) to compensate customers wrongly sold PPI alongside loans and mortgages in one of the country's worst consumer financial scandals.

Policies were meant to cover repayments if customers fell ill or lost their jobs but were often sold to people who would not have been eligible to claim.

The Central Bank of Ireland said it has ordered the banks, including a seventh lender which asked not to be named, to start contacting customers over the next few weeks, using independent third parties.

It advised customers to wait to be contacted by their PPI seller.

The central bank did not say how many people might be affected but media reports have estimated that 340,000 PPI policies were sold over the past five years.