The building society, which is owned by its customers, said the deal comprises a £2.5bn savings book and a £430m mortgage book.
It added it would also acquire the Egg brand.
The sale of the Egg divisions to Yorkshire Building Society, which remains subject to High Court approval, 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.
Andrew Hagger of Moneynet said: “The UK desperately needs increased competition amongst financial services providers as consumers look for a trusted brand to deliver on both rates and service.
“Yorkshire BS, the second biggest mutual and growing fast, having already tied up with Chelsea BS and Barnsley BS and currently awaiting approval for a merger with Norwich & Peterborough BS.
“The acquisition of a new £2.5bn savings book will enable one of the most competitive mortgage providers in the UK to expand its lending activities to a much wider audience.”
