Channel 4 is to cut 15 per cent of its workforce, screen more repeats and cut serious programming in favour of lightweight reality programmes such as Big Brother as it tries to head off losses caused by an advertising collapse.

The broadcaster said that it would slash £100 million from its costs - cutting back on current affairs, serious factual programmes and possibly dramas in the rest of this year and in 2009.

The cuts are a reaction to the credit crunch, which has pushed advertising booking down since the summer. Of the savings, £50 million will come from the broadcaster's £600 million programming budget this year and next.

Andy Duncan, chief executive of the state-owned broadcaster, said: “Our objective as a public organisation is to operate at break-even with the maximum creative investment. With revenues falling, we have no alternative but to cut costs.”

Channel 4 will abandon showing new programmes on Saturday nights - usually a home for science, history or other serious programmes giving an alternative to The X Factor or Strictly Come Dancing.

It will also stop commissioning expensive serious programmes on other nights, shows such as Kevin McCloud and the Big Town Plan, a four-part series about the regeneration of Castleford, a run-down former mining town in West Yorkshire. Taking seven years to film, the programme won an audience share of 4 per cent, less than half Channel 4's average.

Meanwhile, its most popular shows, such as Big Brother, Hollyoaks and Deal or No Deal, will not be affected as they generate a disproportionate share of its profit. Channel 4 News and Dispatches, the flagship current affairs programme, will also be protected.

The gloomy announcement came two days before Ofcom, the regulator, is due to release a critical interim report into the future of public service broadcasting. Ofcom accepts that Channel 4 is short of money and will discuss how the broadcaster can be given financial help of £60 million to £100 million a year. It is expected to suggest, as a possibility, that cash could come from the annual £3.4 billion raised by the BBC licence fee.

Politicians indicated yesterday that Channel 4 had to make some kind of savings of its own if it was to qualify for financial help. John Whittingdale, the Conservative chairman of the Culture, Media and Sport Select Committee, said: “It would be unthinkable for the taxpayer to bail out Channel 4 without the broadcaster making any efficiency cuts. I think nobody would want to see Channel 4 disappear.”

The cost-cutting plan will lead to Channel 4 cutting its programming budget from a planned £600 million this year to £575 million and to £550 million in 2009. A further £25 million will be saved from the loss of 150 jobs at the broadcaster's head office, with the remaining £25 million of savings coming from a mixture of reduced marketing and other short-term cutbacks.

Rival broadcasters privately questioned whether Channel 4 had done enough, saying that its overheads remained high for a broadcaster of its size. They were also critical of Channel 4's decision to spend £12 million a year on buying new digital radio frequencies on which it is yet to broadcast any services.

Channel 4 said that advertising bookings were down 17 per cent in September. Bookings are also down 5 per cent in October and between 7 and 10 per cent in November.

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