Professor Martin Earwicker, director of the National Museum of Science and Industry group, told The TES that school trips needed to be viewed "not as a reward but as a motivator".
Professor Earwicker was due to use his speech today to call for the Government to recognise informal learning, through visits to museums and other activities, as an "essential part of education".
He described the science curriculum as "narrow in focus" and criticised government for its purist view that education only happens in the classroom. "We need to allow children to find out more for themselves," he said. "There are limitations about what can be covered in the classroom."
He said some pupils were never going to be motivated by the traditional academic style of learning. "We are at risk of losing these children," he said. "And once we have lost them, we have lost them forever."
Professor Earwicker, who worked for the Ministry of Defence as chief executive of the Defence Science and Technology Laboratory until 2006, said that it was a trip to London's Science Museum that inspired him to become a scientist. He is now head of the museums group, which includes the Science Museum, the National Railway Museum and the National Media Museum.
But while teachers agree school trips enthuse pupils, they said running many more was simply not practical.
"It is a joy to go on school trips," said Anita Kapila, a science teacher at Burnham Upper School in Slough. "But organising them is such a hassle ... getting the transport, collecting the money and sending out the letters." Parents also raised concerns about the financial burden.
"Learning outside the classroom is a vital part of a child's education," said Laura Warren, spokesperson for the National Council for Parent Teacher Associations. "But it needs to be accessible for all children."
A TES poll in October revealed that a third of teachers had cancelled school trips. Forty per cent cited cost as the problem and 36 per cent said form-filling had put them off.
The Government responded to criticism last year by publishing a manifesto on learning outside the classroom, pledging pound;2.7 million towards encouraging school trips.