The cable company, which last week revealed that it had failed to stem the tide of customers abandoning its services, is expected to step up its focus on retaining its existing base of 1.76 million cable TV customers.
Figures unveiled last week showed it had lost 5%of its customers in the three months to the end of September.
Telewest wants to develop more effective cross-selling and communications strategies rather than targeting potential customers, and its marketing spend is likely to see increasing diversion toward retention activity.
Rapier is thought to fit the bill because of its credentials as an integrated agency working with brands such as the AA.
While the deal has yet to be confirmed, a split from Saatchi & Saatchi would mark the end of an era for Telewest, which is widely expected to merge with rival cable firm NTL at some point.
Saatchi & Saatchi was appointed to the Telewest business alongside Wolff Olins in March 2000 following the company's merger with Flextech. Since then, it has marketed a range of cable TV, telecoms and broadband internet services. It now operates under the Telewest Broadband and Telewest Business brands.
However, the firm has struggled to compete in the TV market against BSkyB, that last week reported a £14m pre-tax profit and the highest first-quarter subscriber growth in its nine-year history, up 217,000 to 6.32 million.
Telewest has seen significant turnover in its senior management team, with chief executive Adam Singer departing the firm earlier this year.
Telewest's consumer managing director Phillip Jansen left the company to join MyTravel as European chief executive during the summer.
Neither Telewest or Rapier would comment as Marketing went to press.
Telewest's media planning and buying account, held by Media Insight, is still believed to be up for grabs.
Separately, NTL has announced the departure last week of managing director Stephen Carter, who has been linked with the vacant chief executive posts at Emap and Trinity Mirror. Carter joined the cable firm from J Walter Thompson.
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