But Lloyds TSB is not alone. RBS faces similar challenges as it completes its merger with ABM AMRO. Germany's Commerzbank and Dresdner Bank are also joining forces, Barclays and Japan's Nomura are merging with parts of Lehman Brothers, while the Bank of America is swallowing Merrill Lynch.
Choosing which IT system should have precedence is a dilemma. Both Lloyds and HBOS have advanced IT systems, each capable of processing the business of the other bank. And the skills of each IT department are among the best in the world.
The project required the consolidation of 400 business processes, 22 billion customer records and 18 million accounts. It saved £2.3bn, exceeding its target of £1.4bn savings.
One dilemma facing Fisher is to decide the merged banks' outsourcing strategy. Lloyds TSB outsources a lot of its IT compared to HBOS, but in the past Fisher has favoured keeping IT in house.
Organising and merging the data from the two banks will be a bigger challenge, says Justin Speake, CEO at Bloor Research. "The challenge is less about the choice of platform and more about getting all the data in the right place and securing it." The number of systems with "unique foibles"makes this integration difficult. A lot of customer data and business can be lost if systems are stranded, he says.
Lloyds TSB is likely to look at all the IT systems that overlap and make decisions about them depending on their flexibility, scalability and security, says Rajeena Brar, banking analyst at Pierre Audoin Consultants. "We know that a lot of banks are replacing legacy systems so whichever of the two banks is further forward in addressing this will be a key factor."
The merging of two IT infrastructures is an opportunity to save money and update technology for banks which have had legacy systems for as long as 40 years. But deciding between the IT of two banks is no mean feat because banks have spent heavily in systems and skills.