The bank said it was cutting the TV network's forecast to 1% from 6% for the year to September 2003 because the expected advertising recovery was delayed, and ITV had lost audience share.
The bank also cut both companies' earnings forecasts by 25% and 24% for Carlton and Granada respectively.
The bank said: "Given the operationally geared nature of these businesses, this results in a downgrade in terms of 2003 estimates and earnings before interest, tax, depreciation and amortisation of 25% for Carlton and 24% for Granada."
The bank added that Carlton's financial situation appeared sound in the long term, but that it would not exclude a credit rating downgrade in the medium term due to a "lack of advertising market visibility and high operational gearing".
Shares in Carlton fell 0.17% to 157.25p, while Granada was up 3.27% to 89.5p in early afternoon trading.
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