The Astronomer Royal says the money should be devoted to robotic missions instead of sending astronauts like Tim Peake into orbit.
Britain's leading astronomer has told Sky News that the public should no longer fund human spaceflight.
Martin Rees, the Astronomer Royal, said the European Space Agency (ESA) should devote its budget to robotic missions - and not repeat Tim Peake's stint in orbit.
"I think the future of human spaceflight worldwide is really only as an adventure and spectator sport," he said.
"As robots get better they can do more of what people were doing in the past. So the case for sending people is getting weaker all the time."
The UK contributed £70m over four years to the ESA's human spaceflight programme.
Lord Rees said that was a "good deal" done by former science minister David Willets and Peake's mission was "worth the marginal cost".
But ESA's budget is only a third of NASA's.
"In the long run the only case for sending people into space is if they are funded by private ventures like SpaceX in the US," said Lord Rees.
"I say that because it's not public money and also because private organisations can take high risks and cut prices at a level that can't be done by publicly funded civilian programmes."
But speaking from the ISS just days before he returned to Earth, Tim Peake said: "This has been an exceptionally worthwhile endeavour.
"This is about the UK becoming involved in human spaceflight hopefully for the foreseeable future.
"Space is going to play an increasingly important role in our lives and if the UK is not in the forefront of that we are missing out quite simply."
More than a million school children have been involved in projects related to Major Tim's mission.
Fullbrook School in New Haw, Surrey, is one of hundreds growing rocket seeds that he took with him to the ISS - and have since been returned - to test the effects of microgravity on plants.