Yorkshire Building Society is to buy the Egg brand and its £2.5 billion savings book and £430 million mortgage portfolio from Citigroup.
The deal is expected to close later this year, at which time Egg savers and borrowers will become members of the Yorkshire Building Society.
The transaction threatens the jobs of the 600 staff employed by Citi to manage the Egg business. Yorkshire will not take on any Egg staff, although an unspecified number will be retained by Citi under an outsourcing deal that runs until the end of 2012.
Citibank acquired Egg from UK insurer Prudential for £575 million in 2007. The US bank has been looking to offload the business for some time as part of its non-core asset disposal programme, instituted in the wake of the credit crisis.
The deal completes Citi's disposal of the direct bank's assets following Barclays' acquisition of Egg's credit card portfolio in March.
Transaction details for both the Barclays and the YBS deals have not been disclosed.