Aegon has said it has completed the technology upgrade of Cofunds' retail book of customers.
The upgrade took place over the Bank Holiday weekend and saw more than 400,000 users and £37bn of assets upgraded to the Aegon Platform.
This was the third stage in the integration of Cofunds with Aegon, with the Investor Portfolio Service and institutional service having upgraded in December and March respectively.
Mark Till, chief distribution and marketing officer at Aegon, said: "After a busy weekend, we are pleased to confirm the technology upgrade has completed. Intermediaries and their clients will from today start using the new Aegon Platform.
"A number of advisers took part in the upgrade testing this weekend, logging into the system, accessing their customer records, and reviewing valuations and models amongst other tests.
"We know that with such a major upgrade of our platform we’re expecting many users will want to login so we’ve made every effort to ensure we can meet high levels of demand on our website and contact centre, but we expect the first few days of operation to be exceptionally busy.
"This upgrade is the culmination of a huge amount of effort, and significant input from intermediaries and their teams. It'll be a long time before Aegon does anything of this complexity again or which touches a greater number of customers and intermediaries.
"At launch we will be listening carefully to feedback from advisers and aiming to help them become familiar with the platform and embed it as part of their daily business."
Aegon bought Cofunds in 2016 for £140m and has been planning the integration of the two platforms ever since.
Over the course of the integration process nearly £100bn in assets has moved from Cofunds to Aegon, which had £22bn on its own platform.
The core of the new platform is based on the Aegon Retirement Choices system but the company has promised to include the best of both services.
Aegon worked with an advisory board made up of 30 advice firms of various sizes to find out what they want from the new platform.