What lenders need to know about mortgage book migration

For lenders, moving their mortgage books from one software provider to another can be a complex business, as the two operating platforms will be different.

The ultimate goal for them is that all the data can be moved seamlessly from the source system to the new platform, so business can continue as usual the day after the completed migration.

The opinions expressed here are those of the authors. They do not necessarily reflect the views or positions of UK Finance or its members.

Many lenders want to move from a legacy system to a new best of breed platform. However, it can be a daunting task, so they often stick with the clunky platform they are used to. The way to gain confidence about migration is to talk to the software provider and ask a myriad of questions so you know exactly what will happen and when. By working closely and taking steps to mitigate potential challenges, lenders can successfully move their mortgage book to a new provider and reap the benefits of improved technology and efficiency.

What is absolutely critical to a successful migration is a detailed schedule of events, as well as regular communication and progress updates. We at Phoebus have carried out hundreds of migrations, so here are some of the main things we believe lenders should consider.

Migrating the data

Data can be migrated in three main ways – functionality driven, quantity driven or big bang. Based on the testing strategy, for a portfolio you could move tranches of accounts with full system functionality, or all of the accounts with trickled down functionality, or a big bang of all the accounts with full system functionality.

Data mapping

Cleaning the data so it is ready for migration and will tally up at the other side is a vital part of the migration process. You will need to know if the new application can hold data in the same format as the system you are migrating from. If it can’t do that, then how will you cross reference back to your previous system? 

Data fields such as account numbers, customer references, addresses and products must be cross referenced as well as all the transactions such as payments. How will you map your existing transactions to those in the new system? 


The testing phase is critical to any migration or boarding activity, what you start with and what you end up with after the migration have to be the same. So it’s best to ask about the documented testing strategy –how many dry runs and dress rehearsals of the migration will there be?

How will you validate that the migration has been successful? The number of accounts boarded must be equal to those extracted; the number of transactions must be the same; the book balance has to be exactly equal; the number of securities/properties is equal; the number of customers, solicitors and other third parties is equal.


What happens if things go wrong, and the accounts don’t match up? We always recommend an exit plan for the boarding process, so you can fix minor issues then re-run it, or stop the process to allow time to analyse the issues and re-run the boarding later. This involves taking a snapshot or copy of the system before any boarding activity starts so you can roll back to the starting point.

NB: UK Finance adds that the lender should make sure it has informed the FCA and/or the PRA when it is planning on undertaking the migration. This is as it is better to be advised in advance if something has not gone as planned, rather than having to tell them after the event.

Find out more on the Phoebus website.

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