Mr Major sent a copy of the letter to Michael Green, chairman both of ITN and of Carlton, one of the ITV companies that supports moving the news to an earlier hour.
'I am particularly concerned that one of the strengths of the ITV network, the provision of authoritative news programming, may be seriously impaired if the main evening news is not a central part of the schedule,' Mr Major wrote. 'It is important that Channel 3 continues to provide a high quality news service and that it competes effectively with the service provided by the BBC throughout the peak viewing hours.'
The ITC's power to rule on scheduling was curtailed by the 1990 Broadcasting Act, based on free market principles and drawn up by the Government of which Mr Major was a member. Although he emphasised 'the Government does not seek to intervene in programme content or the editorial judgments of broadcasters', the Prime Minister's letter is bound to influence the chief executives of the 15 ITV companies when they meet to consider the change next Monday.
Their plan to broadcast the main news at 6.30pm or 7pm, instead of 10pm, has already raised protests from the Labour leader, John Smith. 'Were this plan to go ahead, it would be a major blow to the coverage of news and current affairs on British television,' Mr Smith said in a letter to Sir George Russell. Ann Clwyd, Labour spokeswoman on national heritage, is hosting a protest lobby at Westminster today.
The switch was recommended unanimously by representatives of the 15 ITV companies at a strategy meeting last week. They were swayed by research carried out by Granada, the north-west England franchise holder, on the extra revenue they could earn by freeing the 10pm slot for drama.
Since then, though, some of the companies have had second thoughts and are worried about the impact of the change on the rest of the schedule. The political pressure will increase these doubts, because the industry needs the Government's goodwill - for instance over the rules barring mergers between large companies, which they are pressing to have relaxed. The feeling is growing that at Monday's meeting the chief executives will shelve the decision.
The ITC is taking legal advice about whether it has the power to enforce the companies to keep the news at 10pm. Since the commission's authority under the 1990 Act is unclear, any such order would be challenged by the companies in court.
Tonight a group of ITV chief executives are having a working dinner with Sir George Russell - one of a regular series - at which they may go some way towards resolving their differences.