Frank Zimmerman and me: The truth about the troll who tormented Louise Mensch

The call from Louise Mensch, one evening last August, was guarded. She had no idea who I was and, as an MP increasingly in the public eye, she was becoming used to the unwelcome attention of strangers. Indeed it had been precisely that which had caused me to contact her, by email and Twitter, the previous day.

She had just gone public about a threatening communication she had received. An email, purporting to be from the powerful computer hacking group LulzSec, which had been much in the news, had threatened to kill one of her children if she failed to get off Twitter. At the time, she was in America, away from her children, and spent the night talking to the police in England and had then tweeted her defiance online. "Get stuffed, losers" was the burden of her message.

The email, I told her, had nothing to do with hackers. I had received a very similar threat the previous week and I knew exactly who sent it. He went under the name of Tim Cavendish, who sometimes called himself the Duke of Cavendish, and on Twitter he also used the alias "Wobert Wedford". His real name was Frank Zimmerman.

I did not intend to write about Frank, who was given a six-month jail sentence this week, suspended for two years. His is a sad story which, had it not involved high-profile figures, would have passed through a county court largely unnoticed.

It was some of the press coverage, and accompanying comments online from readers – nasty, ignorant, hate-filled – that changed my mind. "Sick saddo", they wrote. "Utterly disgusting... let's hope this filth spends some time in nick." His age and unkempt appearance were the subjects of cackling contempt. The word "evil" was a favourite.

It was as if Frank belonged to another moral universe to the one the rest of us inhabit, as if the online bullying of which he was convicted had no connection to the bullying of this sanctimonious mob. I knew that was not the case.

Frank Zimmerman, his wife and two young daughters, lived next door to my family and me during the 1980s. They were perfectly charming neighbours – friendly, quiet, normal. Because we both worked from home, Frank and I saw each other regularly, playing tennis now and then, chatting about our respective careers.

Frank, who was in his thirties, had recently left an office job and was developing some kind of office-planning consultancy from home. He was a restless business type, forever talking into a huge mobile phone, referring now and then to some great deal he was about to close. He was something of a fabulist, but that was the tone of the time.

He did, admittedly, go a bit far in his efforts to keep up corporate appearances. He put shop display mannequins around his dining-room table so that, when seen through net-curtains from the street, the impression would be given that a meeting was taking place. When expecting a call from Canada, he asked my wife Caroline whether she would pick up the phone, say "Zimmerman Associates... Yes, just putting you through" as if his house were a busy office. She declined.

Time passed. The Zimmerman marriage broke up and, soon afterwards, Frank moved out, and I never expected to hear from him again.

"Hi, Frank here."

The call came out of the blue about five years ago, and was a surprise. After my own divorce, I was now living in Norfolk, but Frank's tone was of someone who had been chatting to me on a daily basis.

If I remember rightly, he was in search of professional advice. He told me that he was writing now – people had often told him he had a talent for comedy. His voice was as chirpy and confident as ever but, as the conversation progressed, it became clear that something was awry. He spoke of his friendship with Charles – Prince Charles. He had been left several million pounds in Princess Diana's will, he said.

It was a weird conversation – perfectly amiable but also quite bonkers. Out of misguided politeness – and, I confess, curiosity – I failed to challenge any of his stories, something I have subsequently regretted.

Last July, I heard from him again. In his usual brisk, matter-of-fact tone, he told me that Frank Zimmerman was not his real name – he had assumed it while on the run from his father during his teens. The "Frank" came from Sinatra, whom he had always admired, and the "Zimmerman" because he used to play drums for Bob Dylan, whose real name was Zimmerman.

He was, in fact, Tim Cavendish and when I called him "Frank", he would correct me testily. He needed my help, he said. He wanted to get in touch with Jemima Khan who had recently joined The Independent. He had spoken to the editor's PA (whose name, rather alarmingly, he knew) but the contact she had given him didn't seem to work. Did I have an email address for Jemima?

I didn't. Frank said he would ask Hugh – Hugh Grant – next time he played golf with him. He was living in Provence, he said, and when I asked where, he said, "Hang on. Darling, where do we live?" He was living with a young French girl these days, he explained. She was called Marie-Claude.

So it went on. He was writing a lot now, and liked to contribute to message-boards. He mentioned that he had had his say beneath Hugh Grant's "The bugger, bugged" piece in the New Statesman, both under his own name and, amusingly (he thought) under the name "Henry Root", the enraged fictional letter-writer created by the late Willie Donaldson. I checked later, and there were his messages – angry, feebly facetious, but not that different, to tell the truth, from others on the same board.

I became slightly worried when, that week, Tim Cavendish loomed up on Twitter. He was mildly rude about me, and I noticed that he was following several of my friends. Another tweeter, Wobert Wedford, appeared, and references to our conversation made it clear that it was Frank. Tim and Wobert were soon chatting away with – or rather at – celebrities on Twitter. He invited Piers Morgan to dinner at La Grenouille "(on me!)". He offered to buy the island of Necker off Richard Branson. He told Alastair Campbell that he wrote Four Weddings and a Funeral with Richard Curtis. His tweets to women, most of which were subsequently deleted, tended to be leadenly flirtatious and, if rebuffed, he became nasty and threatening. I must have been worried by Frank's activities on Twitter because, before I went on a week's holiday, I warned some of my friends who used it – those of whom Frank would have heard – to be wary of being approached by him.

Soon after my return, he rang again. He told me he was fed up with Rupert (Murdoch) and had decided to take over News Corp. It had been the last time he had seen Rupert which had done it; he hadn't even been offered dinner. His people in Geneva were working round the clock on the bid.

After listening for a while, I made an excuse and said I had to go out. He was busy too, he said quickly – he was in Martha's Vineyard and the Spielbergs were coming to supper any moment.

Later that night I received an email. It was apparently from LulzSec and in the subject box, read "YOU have been HACKED and are still HACKED, again and again :D". There followed a enraged rant warning me to get off Twitter, mentioning, with names and details, my partner, my ex-wife, each of my children and my grandchildren, and closing with the LulzSec logo. It was threatening and sexually violent.

I now see it as absurd – "You smarmy, smug, sarcastic, POMPOUS little OIK and S***" is probably not the way a hacker would write – but in the hour or so during which I thought it really had come from LulzSec, about whom I had recently written, it was alarming.

It had to be Frank. Who else would use that old-fashioned public school insult "oik"? I made no response, but kept an eye on the activities of Tim Cavendish and Wobert Wedford on Twitter. I noticed at some point that Frank had become fixated on Louise Mensch. She must have decided to ignore him because suddenly his messages to and about her became misogynistic and nasty, one lasting for over 30 tweets. A few days later I read that the MP had been hacked by LulzSec.

I contacted her. When eventually we spoke, I gave her Frank's real name. The following day, three officers from the eCrime unit of the Metropolitan Police drove to Norfolk to take a statement. Frank, it turns out, was known to them. The house where he lived, I was later told, was as squalid as any they had seen. Frank claimed to be agoraphobic and the evidence bore out his claim. He rarely emerged from the house, ordering everything through the internet.

Three times he was called for the magistrates, each time failing to appear. Finally, the police collected him and he was found guilty of sending an electronic message that was "grossly offensive or of an indecent, offensive or menacing character".

After that final hearing, photographs of him, wild-eyed and with long grey hair and beard, like something out of the opening credits of Monty Python, appeared in the press. It was a good story. The man, it was said, even looked like a troll.

Yet there has been something troubling about the whole story. How deluded was he? The police, who have been commendably clear-eyed and effective throughout, have found that he was quite canny in the way he used the system; the term "mind games" was used by one officer. As soon as he was arrested, he dropped the illusion that he was Tim Cavendish. There was no reference in court to his imminent takeover of News Corp. As an agoraphobic, he was spared jail.

I suspect that there are more people like Frank than we like to think. Battered by life and disappointment, they discover that the internet is a playground for their delusions, feeding their fantasies while offering them an anonymity and power to frighten and bully which is denied to them in the real, physical world.

Disturbingly, Frank – or Tim or Wobert – has ended up in the headlines, beside the famous people with whom he once pretended to be friends. In a perverse way, his fantasy has been realised.