Bradford & Bingley's savings business will be the latest to be integrated into Banco Santander's global banking platform, Partenon, after the banking giant agreed a £612m takeover.
B&B will join UK financial services groups Abbey and Alliance & Leicester as part of the Santander group.
The Bradford & Bingley deal will create a combined UK company with 1,286 branches and will give Santander 10% of UK retail deposits with 24 million UK customers.
The remainder of Bradford & Bingley, including its mortgages business, will be under public ownership.
Ralph Silva, analyst at Towergroup, said Partenon puts Santander in a strong position during this period of consolidation.
"It is likely it will continue on this acquisition spree," he said. "Imagine if there is something you have always wanted and they are on sales, there is no way you would say no."
"Partenon could be a differentiator because it gives Santander the ability to more easily and more quickly integrate acquisitions," he said.
Santander is expected to make significant savings in IT through integrating B&B's IT systems into Partenon.
The bank completed the integration of Abbey to Partenon in the summer, a key element in its plans to reduce costs at Abbey by £300m.
It also announced its intention to acquire Alliance and Leicester for £1.3bn in July and expects to make efficiency savings of between £30m and £50m by integrating it with Partenon.
Santander sees Partenon as a route to creating a single view of customers across all financial services units such as current accounts, mortgages and loans - a long term goal of all banks.
Santender's move comes as consolidation in the UK banking sector is gathering pace. Its take over of Bradford & Bingley follows news that Lloyds TSB will acquire HBOS.
Bradford and Bingley announced last week that it was closing a mortgage processing centre to cut costs. About 300 call centre staff will go at the processing unit in Hertfordshire and the work will be transferred to a centre at Bingley in West Yorkshire.