Some people you don't forget.
I bounced into a smart London reception, whip-thin women were wearing short, chic, black silk. I was in long, brown tweed. I felt like a Highland cow.
I was still young enough to mind so when I spotted one other tweedy brown suit across the room. I was drawn to the man wearing it. He was roundish, fun and friendly. We were chatting pleasantly when the ambulance drivers' strike was mentioned. It was 1990, the Thatcher era and I said I thought she was losing the plot.
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My companion reared. What did I mean, he asked? I told him that people loved ambulance men and didn't love the Iron Lady; that she had lose this fight.
Well, I would tell you what he said except it was so fast and fluent and well informed I can't remember a word of it. I stood my ground but it was akin to a field of wheat standing up to a combine harvester.
Later, as I was leaving, I passed him and he good-humouredly thanked me for an interesting conversation. "Who was that?" I asked my companion. "He knows a heck of a lot about Conservative policy."
"He would," she said. "That's Alistair McAlpine, the Tory party treasurer."
Why am I telling you about this minor brush with the peer who has triggered the largest-ever legal action against those who erroneously associated him with paedophilia? It's because, even after all this time, the moment I heard the accusation against him I said: "I don't believe that man is a paedophile."
I know. They don't come with a capital P tattooed on their forehead. But neither are they relaxed, take-me-or-leave-me, big characters with full lives. When Jimmy Savile was accused it didn't surprise me. He was a hollow man, the antithesis of Lord McAlpine.
Having once witnessed Lord McAlpine's rapid response to my challenge, I'd have warned tweeters to beware. He was never going to take rumour-mongering lying down. And why should he? He told the Radio 4's World at One last week of his shock, disbelief and conviction that "this is happening to somebody else".
He said: "Newsnight confined me to the lowest circle of hell. It gets into your bones ... and it gets into your soul. You just think there's something wrong with the world."
Which of us would feel differently if we discovered 10,000 strangers spreading the lie that we were a child molester? In this society we believe things we hear repeated. It's how advertisers get us to buy things – by repeating their message. Lord McAlpine's good name has been smeared across the globe. No wonder he fears his reputation will be forever tainted.
But you don't have to be famous to have your life turned inside out by the speed and ubiquity of modern social media.
Neda Soltani was a Professor of English literature in Iran. Unknown to her a young woman with a similar name was shot dead by government forces during a street protest in 2009. The media, rushing to meet the demands of rolling news, muddled the two women. They lifted the English teacher's Facebook photograph and instantly she became the emblem of the protest movement.
People across the world were carrying her face on placards, lighting candles in front of it, creating shrines around it. She said it was like watching her own funeral.
When she tried to explain it was a case of mistaken identity, the protesters said she was an agent of the state assuming the dead woman's identity to pretend she was alive. When she wouldn't help Iran's Ministry of Intelligence, the state said she was in the CIA. She had to bribe her way out of the country.
She has written: 'To live the life of a refugee is to be a leaf in the air. I am still suffering from depression. I am still suffering from nightmares."
Two people and two lives blighted by slip-shod standards of proof and the speed with which social media can spread inaccurate gossip.
Each person who tweeted or posted on Facebook was probably guilty of nothing more than wanting to be seen to be in the know. I doubt any of them would dream of calling someone a paedophile to their face without cast-iron proof. And if they did make the accusation they'd expect a punch on the nose.
So why do they think it is acceptable to tweet the slur? And what made them imagine there would be no repercussions? Trashing someone's character is not a victimless crime. I think when professional journalists set hares running, the public presumes they're safe to pass on. They presume facts have been checked – especially when a programme as reputable as Newsnight is involved. Also they think there's safety in numbers.
So do tweeters deserve Lord McAlpine's wrath?
I'd say he's pitched his retribution perfectly. If the average person apologises he or she gets off with a small fine paid to charity. It's not punitive but a lesson has been learned. Those who should know better – and who command bigger audiences – he's hitting harder. The publicly funded BBC is paying £185,000, reputedly a much smaller sum than ITV will be asked to pay.
Lord McAlpine's actions are a wake-up call. We talk about free speech but as everyone involved with newspapers or television knows, there is a limit to what can be safely said about any individual. Damaging accusations have to be based in fact and provable.
Is Lord McAlpine right to pursue those who so casually passed on the accusation against him? I think so. This is about protecting people from false and ruinous accusations.
What would have happened if he'd been a retiring man of modest means? I think we all know the answer to that. Without the ability to crush the mob's accusation, Lord McAlpine would have been in considerable personal danger.
If his deft and determined action puts down a marker that makes people think twice before they tweet and pass on hurtful rumour, he'll be a force for good. He'll be striking a blow for people weaker and poorer than himself, whether they're schoolchildren suffering from cyber bullying or an Iranian English professor who suddenly finds herself the victim of mistaken identity.
Some good may come of this mess after all.