FOR the internet giants, the heat is on.

Culture secretary Maria Miller is to call companies such as Google, Microsoft and Facebook to a summit where she'll demand closer industry-wide co-operation to prevent the transfer of internet horrors such as illegal pornography, images of child abuse and material that could incite religious or racial hatred. She was spurred by recent tragedies: the Woolwich killing and the fact that April Jones's murderer, Mark Bridger, had extreme and child pornographic material on his computer. Miller's aim, says one of her aides, is "to get all these people in a room to explain what they are doing. It's not good enough for them to throw up their hands and say: "It's all very difficult."

But perhaps the truth is that regulating the web is very difficult. And perhaps there are costs to censorship systems that many of the UK population might think aren't worth the benefits. As anxiety also rises about children's exposure to internet porn, with increasing calls for the kind of opt-out national filter on pornography that Communications Minister Ed Vaizey proposed in 2010, we need to acknowledge the nature of the internet beast.

Perhaps the notion of a porn-free world is just wishful thinking. Even if it is feasible, we might have to sacrifice too much in terms of free speech and liberty to gain it. Think of an internet life lived always within the confines of a workplace filter, and imagine that filter tightening up, blocking things that you never dreamt offensive. Of course, some might say that for the sake of our children, and ourselves, it is worth the sacrifice. But we mustn't pretend that the sacrifice does not exist.

Neither must we pretend it only requires a flick of a switch. There is no simple route to blocking access and movement of such information. Author Ben Hammersley, in his book Now For Then: How To Face The Digital Future Without Fear, points out that "a surprisingly high proportion of Western politicians have not grasped what their Chinese opposite numbers have learned: there is no such thing as light-touch censorship online".

Although filter mechanisms exist, these tend to be prone to both under and overblocking.

When, in 2009, WikiLeaks leaked the blacklist of addresses created by Australia's communications regulator for use in filtering software, it revealed not only child pornography sites, but also online poker, fringe religions, fetish, euthanasia, and even the site of a Queensland dentist.

That said, we are on the slippery slope to a more filtered world. Internet service provider (ISP) TalkTalk has an opt-in network-level scheme filtering out pornographic and obscene material, and other major providers such as BT and Virgin Media are following suit. Generally, the process involves parents choosing to opt in to a filter that makes the whole home, and all the devices within it, "safe". But the fact that these are "opt-in" is contentious. Many would like to see schemes, where you have to say "yes" to porn, rather than "no" to avoiding it.

Few are proposing that the UK instigate a national no-option filter, but given the mood in the country and among politicians, it would be no surprise if one were mooted.

And what argument could there be against filtering something as vile as that? In Thailand, a national filter intended to stop the spread of child pornography was modified to block sites criticising the royal family; it could be argued that filtering helps to erode free speech.

Meanwhile, in Iceland, there is a bid to block all online pornography, but there has been little explanation of how it will work. Government adviser Halla Gunnarsdóttir says she wants to "explore all possibilities and take a political decision on what can be done and how". In other words, "what and how" are still unclear. Suggestions being explored include web filters, the blocking of addresses and criminalising the use of credit cards to pay for pornography.

But when all these methods are examined, their limitations are exposed. Mechanisms for blocking the transfer of information are complex. Even when they do work, there are, for those who know how to access them, areas known as "the dark net" where all that is banned and blocked still exists.

There is something about the frequent calls for more filters, blocks and bans that smacks of statement politics, of people who want to be seen to be making a difference, rather than really doing so. We already have a system, if an imperfect one, for blocking child pornography. The Internet Watch Foundation takes reports from users of the internet who stumble upon child sexual content and feeds these to ISPs, which block the sites. We should bear in mind that many technology experts, such as Hammersley, believe that the best way to close down child porn sites is through police enforcement and entrapment.

Of course, the corporate giants that dominate the internet evoke little sympathy, and few would like to see them squirm out of responsibility or avoid measures because they are too costly. But attempts to control the internet should be approached with caution.

When we hear calls, such as Theresa May's in the wake of the Woolwich killing, for a reinstatement of the so-called snoopers' charter, which would require ISPs to hold information on the movement of personal communications of UK users for 12 months, we should be realistic about what difference this might have made. MI5 were already aware of the Woolwich suspects. It did not need wider surveillance measures to uncover them.

And if what we are scared of is the radicalising power of the internet, we should consider that actually it is not in the virtual world but the real one that this mostly occurs. One study by the International Centre For The Study Of Radicalisation And Political Violence found that in only four or five reported cases in Europe had radicalisation taken place purely over the internet.

Not everything exists online. Much of what is truly horrifying is out there in the real world. And it is, above all, in that world that we should counter it.