They make for an unlikely double act. One is a knight of the realm and a one-time controller of BBC2 with more than 60 years of broadcasting experience, the other a former member of the pop group D:Ream turned particle physicist.

Sir David Attenborough and Professor Brian Cox made their debut together not on screen but in front of the Lords communications select committee on Tuesday, in which they held forth on topics from climate change and TV fakery to the licence fee and cuts to the BBC World Service.

Appropriately for the senior member of the partnership, Attenborough was most outspoken about the challenges facing the BBC. He said the salaries it paid its senior executives were too high and that it spread itself too thinly across too many TV and radio networks.

"Sometimes it thinks it has an obligation to do everything, it should think of focusing more than it does," said the 85-year-old natural history presenter.

Attenborough said the BBC's channels did not have the character they once did, with responsibility for commissioning programmes spread than when he was in charge of BBC2 half a century ago.

Not that Cox was a shrinking violet: the Wonders of the Universe presenter condemned government cuts to the funding of the BBC World Service. "I think it's a ridiculous thing to do personally," said Cox. "It is one of the most powerful foreign policy instruments this country has."

The Manchester University professor said the BBC's licence fee should be set by an independent body in the same way that the Bank of England sets the interest rate. This after the licence fee was reduced by the government by 16% in real terms when it was frozen until 2016, with the BBC given extra funding responsibilities – including the World Service. "For me the BBC will become weaker the more it feels under threat by whichever government is in at the time," said Cox.

Both men were full of praise for the corporation – "What the BBC offers can't be paralleled in the present broadcasting landscape," said Attenborough – although the veteran presenter expressed concerns about the impact of new technology on the veracity of what viewers were seeing.

He said digital reconstructions of creatures that died out millions of years ago, or of species which were not possible to film because they were so far deep down in the ocean, risked confusing viewers who did not know what they were watching was real or not.

"If I wanted to show a fish from the abyss that nobody's ever seen alive, but they fished it out and put it in a tank with coral or something but it's dead, it's not difficult now to use a computer to make it waggle its fins," Attenborough told the Lords. "That's false, but it's also true."

But he said a solution was not as simple as having a "red spot" on the screen to indicate a reconstruction. He added that he had "some misgivings" about a sequence in a recent episode of BBC1's science programme, Inside the Human Body.

"If you've got to put a red spot on everything, spots would be coming and going, then there would be half spots. I think it's a very real problem. If you wanted to confuse an audience there are more convincing ways of doing it than ever in history."

Cox said the BBC should not be afraid of making mistakes and should be more confident about itself. "A broadcaster that does not make mistakes is not trying hard enough," he added.

"I would like to see it more on the front foot. The way it delivers the best possible programming is not to be scared to make quite serious mistakes and make many mistakes because that's the way it comes a creative organisation. I would like to see it more confident."

Cox said the BBC should be biased "only in favour of good science", adding that there was a prevailing scientific consensus on issues such as climate change that should form the basis of its programmes.

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