An ntl spokeswoman confirmed Weber Shandwick had been 'brought in to strengthen our public affairs capability' but refused to comment on details.
She added that LLM Communications, the company's PA agency for the past three years, would continue to be retained, working alongside WS.
A merger between Britain's two biggest cable companies has been mooted for several years. But ntl's poor levels of customer service and high debt have stalled negotiations.
The company's business situation has improved, however, with three million subscribers to its cable TV, web and telephone services.
Ntl will need to convince Ofcom, the Department of Culture, Media and Sport and the DTI that merging with Telewest will not counter Britain's commercial and consumer interests.
It will stress that a deal is minute compared with the Carlton/Granada merger.
Two other agencies pitched for the merger brief. WS will report to ntl public affairs director Paul Richmond and director of communications and policy Keith Monserrat. WS MD of PA Jon McLeod will handle the account alongside head of European PA Wilf Weeks and corporate and PA director D-J Collins.