Danske Bank, the owner of National Irish Bank (NIB) and Northern Bank, is in the process today of migrating 1.1 million customer accounts to a new technology platform.

The complicated procedure marks the culmination of a full year's work for the bank, which took over the Irish operations of National Australia Bank in February 2005.

Danske has estimated the conversion costs at €200 million, with €70 million of this relating to NIB and the remainder to Northern Bank.

About 4,000 employees of the two banks are due to work all weekend, with the process scheduled to be complete by Monday morning.

Kevin Gallen, deputy chief executive of NIB, said the staff, who are missing out on the long Easter break, "fully appreciate this is a once-in-a-lifetime experience".

As well as converting the 1.1 million customer accounts, with the direct debits, overdrafts and other facilities these might carry with them, Danske is launching new websites for both NIB and Northern over the weekend.

These will include new "e-banking" services for business customers.

On top of this, a new customer contact centre will become operational in Belfast from Tuesday.

The banks will remain closed to customers on Monday, but staff will be able to start using the new technology with real accounts to make sure that the migration has occurred without glitches.

The new systems will also be used on Monday to handle procedures such as lodging of night safes from the weekend. On Tuesday, it will be fully live for all customers, with the two banks also set to launch their strategies that day.

Mr Gallen could not provide a breakdown of customer numbers between the two banks, but it is safe to say the greater number is connected with Northern Bank.

Northern has a 20 per cent market share in Northern Ireland, while NIB holds a much smaller portion of the Republic's banking market.

Danske is unique in large-scale European banking for placing all of its operations on the same technology platform.