There is nothing as terrifying in all the academic world, says one scientist; it is like going to the guillotine in a cart that you cannot stop, says another. Agreeing to give the Royal Institution Christmas lectures takes up six months of your private life and subjects you to large quantities of stress.

Flung for a few weeks from academia into television, this year's RI lecturer, earth scientist James Jackson, will today be half-way through the filming of his lectures. The process has unnerved the United Kingdom's most outgoing scientists as the BBC has turned it into a high-tech production to compete with sparkling Christmas and New Year schedules.

Dr Jackson, from Cambridge, is lecturing on "Planet Earth, an explorer's guide". When the huge TV vans with thick spaghetti of wire hanging out of them arrive, you realise how deadly serious it is, the old hands say. Dr Jackson has to manipulate one demonstration a minute for five lectures.

Yet he wrote his lectures this summer, under the light of a hurricane lamp beside his tent in outer Mongolia.

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The lecturers are chosen by BBC talentspotters at public science lectures, says Caroline van den Brul, of BBC science and features.

The chosen scientist is first asked to produce five 10,000-word scripts. Dr Jackson said: "You suddenly realise there are huge parts of your subject you have always bluffed your way in."

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James Stirling, professor of organic chemistry at Sheffield Univeristy, who gave the lectures in 1992, refused. "Chemists don't use scripts. There was creative tension between the producer and me."

When Michael Faraday launched the lectures 166 years ago, there was probably less stress. But Faraday's maxims persist: speak for no more than an hour and ensure that "the path be strewed with flowers ".

After three months of work and two weeks of filming, when the last flower has been strewn, the film crews disappear and the washed out scientist is abandoned in the ancient lecture hall. For some, their life has been changed permanently. Susan Greenfield, who lectured on the brain last year, has been all but gobbled up by the voracious public understanding of science machine.

But Professor Stirling was a little disappointed at the seeming lack of impact of the lectures: "I bought myself a pair of dark glasses so I wouldn't be mobbed in the street," he said.

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But they proved unnecessary. "A lot of people watch the lectures but they are mainly elderly ladies judging by my correspondence."