Carlton's share price had rebounded 68% since it last dipped in October. Investors were reassured when the company issued £398m in exchangeable bonds and there was the expectation of a recovery in the TV ad market in the run-up to Christmas.
However, a broker at Schroder Salomon Smith Barney believed the optimism about the ad market would be short term and downgraded the company's shares on to his sell list.
The broker said it downgraded the stock from "neutral" to "underperform" in the belief that Carlton's "forward earnings multiple is unsustainably high".
Shares in Carlton fell 12.25p on Wednesday to 204.75p, yesterday it fell just 0.25p to 204.5p.
Meanwhile, the company has called on the UK government to relax media ownership rules, which currently prohibit non-EU companies owning more than 20% of an UK terrestrial TV broadcaster.
Speaking to the Department of Culture, Media and Sport's Commons select committee, Carlton said it believed that the 20% ceiling should be relaxed on a reciprocal basis. For example, if a UK company is allowed to own 30% of an Australian or US broadcaster, then an Australian or US broadcaster would be allowed to do the same in the UK.
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