No one would have believed in the last years of the nineteenth century that this world was being watched keenly and closely by intelligences greater than man's."

So starts H G Wells's 1898 novel The War of the Worlds, which continues with a military invasion by Martians. While contact with aliens may be a common theme in science fiction, could it also be a serious topic in science?

Indeed it could. Ever since 1960 with the first serious search for radio transmissions from other civilisations (known as SETI, the Search for Extraterrestrial Intelligence), scientists have been thinking about what would happen if evidence for ET were found. Examples of their efforts include the 2010 Royal Society conference on "The detection of extra-terrestrial life and the consequences for science and society".

Last week the Guardian reported on a recent paper led by Seth Baum of Pennsylvania State University on this topic, categorising some of the possible consequences – ranging from beneficial through neutral to harmful.

So what's the point? We have never seen these Little Green Men, so why expend effort thinking about what might happen?

Scientists have already had to face this problem in real life. An early occasion was in 1967 when astronomers at Cambridge University using a new radio telescope detected regular blips coming from deep space. They were puzzled because no known source should do that. One possible explanation was ET and the director of the group, Nobel prizewinner Sir Martin Ryle, suggested that they should keep quiet about their discovery and dismantle the telescope, because if it was ET then sooner or later someone on Earth would start signalling back, alerting a possibly evil-minded alien intelligence to our existence.

Fortunately, they soon concluded that it was a natural source – they had in fact discovered pulsars. But there is a continuing controversy in the SETI community about whether it is wise to try and contact ET by sending out messages. For example, the main SETI searchers have agreed a protocol for how to spread the news if and when they discover ET, but have not yet been able to agree a common position on the wisdom of sending out messages.

The main problem is the nature of ETs. What are they like? To be able to influence us, they must be more advanced than us, so will they be wise and benevolent, since otherwise they would have destroyed themselves by now? Or perhaps as a result of a Hobbesian all-against-all struggle the only ET now out there has become dominant by destroying any potential competitors. But even if they were evil would they be able to get at us given the vast distances between the stars?

And it goes wider. Is it wise even to use our radio telescopes to try and detect ET? In 1962 the famous astronomer Fred Hoyle and John Elliot dramatised the risk in a TV series "A for Andromeda" starring Julie Christie. A message from ET was detected which turned out to contain instructions for building a computer. After this was assembled it set about destroying the human race, before being thwarted by the scientist hero.

Considering dangers like that, and applying the precautionary principle, should we shut down all our SETI searches?

Can we tell anything about ET that would guide us, first of all in deciding whether to search at all, then in matching our searches to its nature, and finally in whether to send out signals? My own position, as I argued in a paper presented at the Royal Society Kavli Centre last year, is that our total ignorance about the nature of ET means that we cannot say whether listening or talking is good or bad.

For example, sending a message may cause an evil ET to come and destroy us. Alternatively it may preserve us from destruction by an ET that has become aware of us from seeing our cities and is worried by the aggressive nature of new civilisations, but would be reassured by the peaceful content of a message.

We cannot tell which of the many possible benefits and dangers are more likely, and so we SETI folk can go about our business without reproach. But the more thinking, such as the Baum paper, we do about possible outcomes, the better prepared we may be for the actual outcome after the day of discovery, if and when it ever comes.

It may be good to do this, but is it worth spending real money on? Well, in fact very little money is spent on SETI. There are probably about the equivalent of 20 full-time people worldwide working on SETI, most funded from private sources, together with a little money from individual universities, supplemented with a very small amount from governments. And like all high-tech work it has spinoffs, most noticeably the Berkeley BOINC distributed computing system which started as Seti@home, but is now used widely from biotechnology to meteorology. SETI is used as part of university teaching in the sciences, and it provokes thinking in allied sciences from sociology to linguistics.

Regardless of the chances of success, SETI is of real value. But here in the UK, practically no private or government money goes into it. With around 0.5% of the government funds that now go into astronomy (the 1-in-200 effort, I call it) the UK could make a big splash in the Seti world.

Alan Penny is an honorary reader in the School of Physics and Astronomy at the University of St Andrews, using the Lofar telescope to search for low-frequency radio signals from ET