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Although 2,230 call centre workers are likely to face redundancy, BT said no IT staff will lose their jobs.
The project will see BT rationalise its telecoms and IT hardware and provide customer relationship management and knowledge management software from a central location.
The CWU is seeking an urgent meeting with BT's management, and said it will oppose the programme if it does not secure guarantees for the staff affected.
Jeannie Drake, the CWU's deputy general secretary, said, "The introduction of these changes will in many cases cause enormous problems for members, their families and their communities. We want guarantees that BT will provide alternative comparable job opportunities."
Carol Borghesi, director of next-generation call centres at BT, said that consolidating the company's call centre facilities would enable the workforce to make use of state-of-the-art call centre software and provide better customer service.
"BT recognises the need for a well-articulated IT strategy," she said. "With the consistency of services such as CRM which we aim to deliver, the cost of support would be uneconomical across the current 104 locations. It will be much easier to implement the planned developments in a co-ordinated way at fewer sites."