Yesterday was the 50th anniversary of the introduction of a subscriber trunk dialling system that allowed us, for the first time, to make direct long-distance domestic calls without the mediation of an operator. Yesterday, too, two arrests were made in connection with the leaking and publication last month of the BNP's national membership list. Bear with me as I explore an argument straddling both.

Those who heard recordings of the Queen's first trunk call may have smiled at how old-fashioned it all sounds now. But beneath antique trappings, the reality was modern: a huge leap towards instant communication. Since then we have hurtled ever faster towards constant contact with everybody, everywhere, all the time. The land line itself is becoming antique: we have computer links, mobile phone links and, increasingly, video links.

Hand in hand with this increased ease of transmission, goes a development of immense significance. Modern information technology is fast learning not only how to move, but how to filter and to link. We're enabled to select and lasso the information we want; join it to other information; and to group, and herd, and tag the facts, descriptions and people we want. Our potential command of lists to fish in is breathtaking.

Earlier this week a friend e-mailed me (“for a bit of a laugh”) an internet link whereby, just by entering your postcode, you can access a list of all the members of the British National Party living close to your own home, with names, postcodes and their distance from your door. This link has been designed around that BNP list leaked last month, and has been doing the rounds for some days, spreading like a virus.

I tried it for myself, entering my Derbyshire postcode. Within seconds, on to my screen popped a list of names and postcodes. I recognised one of the names. A second click and on the screen appeared a map tracing routes with arrows - walking, driving or by public transport - direct from my door to virtually the garden gate of whichever individual I had chosen to pursue. Using name and postcode and a couple of inquiries I could have been knocking on the door of any one of them within 20 minutes. Or I could have sent a postcard. Or something worse.

And was it a laugh? No. The moment those names and postcodes appeared on my screen I felt a sharp and involuntary stab of shame. I knew at once this was wrong. It was like rifling through someone's desk; or monitoring a private call. Perhaps a first-time burglar intruding, without their knowledge, into another person's home, feels this: the power, the guilt and the thrill of trespass.

The publication of that list of members and their addresses was itself a serious infringement of their privacy. The design of an internet programme that will be of instant appeal to every nosey-parker in the land - and that's most of us - takes the offence further. How would Jews, or Muslim clerics, or pacifists, or Porsche-owners, or naturists, or anti-hunt or pro-hunt supporters, or members of any group that may attract hostility, ridicule or prejudice, feel about attempts to construct and publish a list that identifies names and addresses? The case against has surely only to be stated to be made.

Or does it? What new issue of principle does this raise that could not have been raised in 1808 or 1958? Membership lists of organisations could always be stolen. There have for centuries been means of publication. You could have printed the names and addresses in the national press a hundred years ago. A thousand years ago you could have copied them out and nailed them to a tree. The laws of libel or slander never offered protection from the publication of the truth.

What has changed is not the principle of what may be done, but the effortlessness and speed with which it may be done.

Return a moment to that “where are they?” internet link. The story needn't end at the discomfiture of those on it. The browser who has established the identities and whereabouts of his closest BNP-supporting neighbours can, without lifting more than a finger, recruit and form a new list: a Facebook group of anti-BNP vigilantes. This list can be triggered - again with no more than a few clicks - into forming what is called a flashmob (already common practice) outside any address, at any time.

Lest you think this unlikely, consider a scenario in which a mass-circulation popular newspaper leading a crusade for the public's right to know about locally resident paedophiles, procures from a maverick senior police source the national sex offenders register, and... Well, need we spell it out further? But again, no new issues of principle here. It has always been possible to organise a demo or a lynching, and people often did; the difference is that it was incomparably slower, less efficient, more expensive and harder work.

As a learner driver in the field of internet capabilities, I am only just beginning to understand the vast new potency of access to lists, whether in the hands of governments, businesses or private individuals. I realise how important is the security - or lack of it - of lists in the Government's hands; and what an enormous step would be the creation of a universal list: a national identity card register.

But I'm also having to face a thought I've always resisted. As someone with a lifelong interest in the philosophy of liberty and of law, there's one philosophical anchor I've held to without wavering: that except in very special circumstances we should never be forbidden from speaking or publishing what is true. The test (I've maintained) should not be: is it kind? Is it fair? Is it tasteful? Or even: is it in the public interest? - cloudy notions every one - but that rock of a criterion: is it true? But now I begin to wonder. When publication was a clodhopping business and fact-gathering laborious, personal privacy was protected by a sort of de facto armour. We never had to confront an imagined world where anyone could find out anything about anyone and tell everyone within seconds.

But today, not only have we the means to retrieve and transmit at breakneck speed the fruits of intrusions into privacy, but we're getting frighteningly clever at the intrusion too. Long-lens photography, easily trackable communications, instant mobile phone photography, the facility to record almost anything, anywhere, ease of storage of vast files of information... all this forces me to wonder whether in the past, when practical constraints clipped the wings of free speech, we could tell ourselves (in what we thought an argument of principle) that we recognised no limits to how far it should fly.

We have not that luxury now. What are effectively privacy laws are creeping up on us. And for the first time in my life I'm beginning to wonder whether “Is it true?” can remain the only question.

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