Yorkshire Building Society is to acquire the mortgage and savings business of Egg Banking, a subsidiary of Citigroup.
The deal, subject to approval by the High Court, comprises a £2.5bn savings book and a £430m mortgage book. As part of the transaction, the Yorkshire will also acquire the Egg brand.
The sale comes just a few months after Citi had sold off Egg's credit card assets to Barclays.
Yorkshire Building Society, which has more than £30bn worth of assets, said buying the Egg businesses would widen its products and range of services, and improve the company's funding position.
Yorkshire has not disclosed how much it will pay for the Egg businesses. The acquisition is expected to be completed by Q4 2011.
The Building Society is also looking at Northern Rock, the fully-nationalised bank which the government aims to sell off in due course.
Iain Cornish, CEO of Yorkshire Building Society, said: "We are looking forward to welcoming Egg's mortgage and savings customers to the Yorkshire.
"Continuing to provide them with the outstanding service, administration and value that they have been used to, and which is consistent with our own approach, will be a priority for us and we will work closely with Egg to ensure that customers are kept fully informed throughout this transfer process."
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