Sir David used his presidential address, the set-piece opening event of this year's meeting of the British Association for the Advancement of Science, to launch an outspoken attack on the Government's plans for broadcasting.
He warned that the changes would lead to lower standards and increased costs.
The Government's wish to see greater competition in the making of television programmes was counter-productive, he said. 'There is no evidence whatever that competition in broadcasting has ever reduced costs - and a great deal to show that it significantly increases them.'
Sir David, who was controller of BBC 2 from 1965 to 1968 and a member of the BBC Board of Management from 1969 to 1972, was particularly concerned about the effects on the corporation. 'In the name of cost-cutting, an institution that has produced programmes as efficiently as any in the world, and to the highest of all standards, that has provided this country with two television networks and four radio networks for less than the daily price of posting a first-class letter, is being gravely eroded, the morale of its staff seriously damaged, and the very things that gave it its unique stature and strength destroyed.'
He also decried suggestions that, in future, the BBC might withdraw from programme-making across the entire spectrum of television and concentrate only on serious and less popular types of programmes. Such a proposal would rob the BBC of the widespread popular support that is essential if the payment of a licence is to be acceptable.
Other television networks which had been forced down this road, he said, 'dwindle in support, in zest and become a ghetto visited by few. It is a form if not of suicide then of castration.' Sir David - a freelance broadcaster, most of whose programmes appear on the BBC - said that viewers had not yet felt the full impact of the changes which had already been forced upon the ITV companies, because they were currently using up their existing stockpile of programmes. However, from next year, he predicted that no programmes would be shown in the evening before 10.30 unless they could be guaranteed an audience of at least 8 million.
Science programming would be one of the first victims of the more aggressively commercial regime, he said. 'From next year onwards, no serious science programmes will be shown on independent television at times that most people will be able to see them.'
The Government's drive to ensure that smaller companies produce a greater proportion of television networks' output will hinder innovation and risk-taking in programme-making, he went on. Small companies did not have the libraries, research facilities and access to expert advice which the BBC, in its present form, could provide from its own resources. 'Innovation implies experiment. What a small company needs is programmes that are sure-fire winners. The last thing it can afford to do is to take major risks.'
The one hopeful aspect, Sir David added, was that the Government seemed to have realised that to try to finance the BBC by advertising 'would be disastrous, for there is simply not enough advertising money to support all four television networks and the others which are expected'.
Sir David announced yesterday that nearly pounds 500,000 had been donated to help the financially pressed British Association to expand its activities in popularising science.
Over the next four years, the organisation hopes to double its income, which for 1992-93 is only pounds 873,000. The Wellcome Trust was the largest single donor, providing pounds 265,000 over three years.