Royal London, the mutual insurer, is to acquire Aegon UK's individual protection book of business, subject to court approval.
The deal will see the life insurance, critical illness and income protection policies for more than 400,000 customers transfer to Royal London.
Royal London group chief executive Barry O'Dwyer said: "We are delighted to be welcoming over 400,000 new protection customers and their advisers. Combined with over 900,000 existing customers who already trust Royal London to protect their families against life shocks, this transaction strengthens our position in the UK protection market.
"Our reputation for outstanding customer service means that customers and advisers will be reassured that they are in safe hands."
He added: "The advised nature of Aegon's individual protection customer base makes it a perfect strategic fit. We are strong champions of the adviser community and of impartial advice, and we look forward to supporting advisers through this transaction, making sure there is no disruption to their businesses or to their clients."
The mutual said customers' policies would transfer to Royal London in 2024, following the completion of a court-approved Part VII transfer. In the interim period, Aegon UK will reinsure the portfolio to Royal London, it added.
Royal London said there would be no immediate change for customers or their advisers. All servicing and claims will continue to be processed in the usual way.
