The truth lies somewhere in between.

We do know that there are dangers associated with radio waves, which is why there are safety limits in place. In general these limits are set at a tiny fraction of any signal strength shown of have an effect. And all devices, be they base stations or mobile phones, run at very much lower powers than those specified by the limits.

This is done not out of any great concern for radiation but because the less power a phone uses, the longer its battery lasts. There are exceptions: a recent, reputable, test found an iPhone 11 Pro putting out more than twice the permitted amount. But even this should not be a cause for concern.

Much of the reason for the fear of 5G is that as human beings we are very bad at assessing risk. When you go on holiday you are far more likely to be hurt in the car trip to Luton airport than on the flight to Ibiza.

We discount the danger of the familiar and amplify that of the unfamiliar.

But with 5G there seems to be a much greater level of concern than we have seen for a long time, so it is worth understanding the technology - and risks - better.

What does science say about 5G?

There are more than 24,000 papers on the effects of radio waves. Sceptics will say “Why are there so many if there is no danger?”, while those in favour will say “All those papers and no smoking gun”. You can nearly always determine which side of the debate a paper lies on within the first paragraph. You knew where this piece stood by the end of the second sentence.

And this view doesn’t come from ignoring facts. It comes from having spent a lot of time looking at the research and speaking to experts, not just in radio but in biology and epidemiology.

What we learn is that this stuff is hard. You can look at the big picture and see a decline in insect populations and a reduction in male fertility which corresponds in time with increased use of mobile technology.

But correlation is not causation and without being able to isolate the use of radio and the effect we can’t assume that there isn't something else going on. Of course, we can expose cells in a petri dish to radio waves and see what happens. But this ignores the whole system, and that in an organism with all kinds of mechanisms which have evolved to cope with ill effects, what happens in a petri dish isn’t a useful reflection of what happens in the real world.

What we’d need is to follow a representative group of people with exposure and a second group of those without - who lead similar lives - and then produce a statistically meaningful list of the differences in health between the two groups.

This is called a cohort study and there are some happening right now, but it’s now become impossible to find people who don’t use mobile phones. That means there is no control group and that severely devalues the research. Such observational epidemiological research is a minefield of unknown unknowns. We might see something happening but it’s impossible to determine why, or often even what, is going on.

Is 5G dangerous?

Unfortunately both sides of the debate cherry-pick information to bolster their argument. So while the 5G industry will say that all the frequencies being used for the roll-out are well known, the protesters will say that no testing has been done on 5G at these frequencies. And both are right. The industry divides the radio used by 5G into low-, mid- and high band. That’s below 1 GHz, 1 to 6 GHz and above 6GHz, (typically 20 to 30 GHz).

While using these with the 5G encoding, known as “New Radio”, hasn’t been extensively tested on people and animals, we do know a lot about the effects of these frequencies.

Low-band is what we have had for mobile phones since the 1980s. And considering that more people on the planet own a mobile phone than own a toothbrush, if there was any danger from them we’d certainly know about it by now.

Mid-band is where we find the majority of mobile signals, from 3G onwards. Again these have been in use for decades and are also the kind of frequencies used by Wi-Fi. Note that 5G uses them at much lower power outputs.

High-band is also known as millimetre wave, and this is the focus of the protests. There is already a lot of experience of these high frequencies, because they are used for point-to-point communications – linking things such as outside broadcast TV to base, for connecting people to the internet in rural areas and for satellite communications.

These tend to use dishes which keep the signal in a tight beam from one point to another so exposure of people to these frequencies is minimal. So we don’t have the same epidemiological information as we do with other frequencies. What we do know is that these frequencies are barely deployed. So all the stories about them having an effect on birds and insects fails to understand the correlation.

There are currently no consumer high-band services in the UK although it’s the preferred technology by Verizon in the US. (Given this fact, you might like to know whether you should buy a 5G phone now or wait.)

We also know that the signals are weak. They just about get through glass, don’t penetrate walls and have a tough time with skin because water is a good insulator. So the physics which would link millimetre waves with brain tumours is challenging.

Will 5G kill you? If you meet anyone who says they are certain it will, they are wrong. There is no evidence for this. Can we say it causes harm? Not at current levels. Can we say it’s 100% safe? Not with complete certainty, as there may be something we’ve not discovered yet.

Looking back with hindsight at asbestos and smoking, there were signs: evidence that there was something to be suspicious of. There are absolutely no tell-tales like this with 5G.

So if a 5G mast has just been installed near your home, or you're considering buying a 5G phone, hopefully you understand the risks, and they're not nearly as bad as many protesters are claiming.