Charles Allen's plans to join forces with Carlton could be blocked

Trade & Industry Secretary Patricia Hewitt said she wanted the Commission to look at the plan mainly because of concern about the sale of advertising.

She said she had made the decision on the advice of the Director General of Fair Trading .

"The merger would greatly increase concentration in TV advertising, leaving one firm with more than half of national TV advertising revenue," Ms Hewitt said in a statement.

Advertising downturn

The heads of the two TV companies denied that, by joining forces, they would reduce competition.

"This merger will not affect the competition for viewers," said Michael Green, chairman of Carlton.

"ITV is already one network and advertisers follow viewers and viewers follow programmes."

Granada's chairman Charles Allen added that a united ITV could "grow in the future and deliver for our viewers, advertisers and shareholders".

Both companies have been hard hit by the downturn in advertising.