British Telecommunications Plc said yesterday it plans to launch a mass market Internet access service on Monday. It would say no more than that it will aimed at small businesses, residential customers, and new users to the Internet. It also said it was a possible partner of Italian state-controlled power company Eni, Ente Nazionale Idrocarburi, and that talks to finalize an agreement for it to take over and run Eni’s worldwide telecommunications nets would start shortly.