In future, C&W will focus on more on the business customer, hoping fewer, larger customer will provide it with more profits.
Up to 3,000 UK jobs will go over the next five years as part of the restructuring.
"We will be selling less stuff but making better profits. Think Armani rather than Top Shop," said John Pluthero, the new chairman of Cable & Wireless's UK division.
C&W will reduce its UK workforce from 5,500 to around 2,500.
The news follows the announcement in January that Cable & Wireless will split into an international division and a UK division, a move that led to the resignation of CEO Francesco Caio shortly thereafter.
Competition in the telecoms market has been intense, as IP-based telephony eats into traditional fixed-line revenues.
This pressure prompted C&W to acquire rival Energis in August 2005 for £674 million.
According to the company, costs savings expected from that merger will reach £40 million by the end of March. The acquisition has also added customers such as broadcasting company BBC and supermarket giant Tesco plc to Cable & Wireless's offering.