Britain's Astronomer Royal Martin Rees said sending people into space when robots could do the job just as effectively was a waste of public money, and space exploration should be left to billionaires and those willing to pay for trips themselves.
"I'm sceptical about the idea of a human space flight being worthwhile," Rees told the Lord Speaker's Corner podcast, which features members of Britain's upper house of parliament.
"Now that robots can do the things that humans were needed for 50 years ago, the case for sending people is getting weaker all the time."
Astronomer Royal is now a largely honorary title. It was established by King Charles II in 1675 to advise the monarch and has previously been held by some of Britain's most pre-eminent scientists.
Rees said space travel should only be for those prepared to accept a "very high level of risk", and it should be paid for privately rather than by the taxpayer.
Britain's space programmes have traditionally focused on space research rather than crewed missions.
Helen Sharman was the first Briton to go into space when she joined the Soviet Union's 1991 Soyus TM-12 mission.
She was followed 24 years later by Tim Peake, who flew to the International Space Station as a member of the European Space Agency astronaut corps.
Four U.S. citizens who flew NASA missions were also born in Britain.
Rees, who was appointed Astronomer Royal in 1995, said he didn't agree with Elon Musk's ambition to colonise Mars, but he hailed his achievements in both rockets and electric cars.
"He has done a much better job than the big conglomerates that used to work for NASA in producing efficient rockets, which can be reused, and that will make it cheaper to actually send stuff into space," he said.
