Bradford & Bingley has consolidated its outsourcing deals with BT into a new £140m contract.
Under the 10-year deal, BT will provide managed voice and data services including wide and local area networking to connect more than 550 sites across the UK.
The agreement brings together previous deals with BT, and adds voice and local area network support for the bank's Charcol business.
The deal will also cover collaborative tools, security services and the hosting of Bradford & Bingley's web-based customer services.
Other areas include email services, security services including firewall management, intrusion detection, virus scanning, and web- and mail-sweeping.
In addition BT will supply disaster recovery services, remote dial-up connectivity into Bradford & Bingley's network for the mobile sales force, and managed web infrastructure and web hosting to support the online financial services offered by the company.
The bank's decision follows a strategic review of its supplier base. Last week Abbey National also announced a move to outsource its telecoms infrastructure to BT in a £125m deal.
The benefits to such companies include increased flexibility, cost savings and better services to both internal and external customers, according to Steve Partington, partner relationship manager at the bank.
"The main benefit is that it allows us to concentrate on our core business. It's as simple as that. We can also reduce our supplier base, which will significantly reduce our communications overheads," he told said.
"Outsourcing also gives us the flexibility we require to react to changing market demands. We don't have the capacity to respond and react in a speedy way if we keep these services in-house."
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