The New York-listed company reported a third quarter pre-tax loss of £721m ($1bn/EUR1.2bn) and admitted it had lost one in four of its UK cable customers.
The news led to a downgrade of the company from credit rating agency Standard and Poor's to a B minus from a B plus. It said the company's outlook continued to be negative.
Last month Moody's Investors Service lowered NTL's rating to Triple C from Single B on similar concerns.
Last year NTL had to pull out of its £328m ($474m/EUR528m) pay-per-view rights to Premiership football games because it could not afford to provide the service.
