Virgin Media has pulled its broadband services to homes in Westminster because the BT infrastructure it uses means it cannot upgrade services.
Virgin's broadband and analogue TV services will stop from January 2012.
Virgin Media said it cannot use BT's infrastructure when it introduces further services.
A Virgin Media spokesperson said: "We use BT's infrastructure to deliver services in Westminster and are unable to upgrade the network and deliver our own next-generation digital services at a reasonable cost. We are speaking to our customers now to ensure they have plenty of time to decide on an alternative service or provider and will do everything we can to help them make the switch."
BT would not comment. According to reports the problem lies in the terms of a leasing contract that Virgin has with BT in Westminster.