For 20 months, I stood accused of a hate crime: homophobically motivated common assault. The British Transport Police pursued my case with extraordinary zeal. So too did the Crown Prosecution Service. I was plunged into a world where common sense withered and died.

The nightmare began when I was travelling home to London after a funeral in Kent. I was chatting with a friend on the train when a strange man started shouting at us from across the carriage. ‘Shut up!’ he yelled before accusing us of conducting a sexist and misogynistic conversation at high volume. This was, in his opinion, ‘offensive’.

Brendan O'Neill and Kevin O'Sullivan discuss the real hate crime scandal:

We were bemused. Talking at a normal volume for a private conversation, we were in fact discussing a male colleague, admittedly using the occasional swear word. Jabbing his finger at us, our accuser insisted we were using derogatory language about a woman. We weren’t. I suggested that he might like to stop his tirade. But he carried on screaming at us. When he went to get up, I decided to defend myself by trying to keep him in his seat. I thought it would be safer that way. My friend was 66 and not well. At this point our accuser leapt to his feet and punched me in the face. A playground grappling session ensued. I’m no fighter and nor was he. It was a non-event, handbags. No one was hurt.

Someone had dialled 999, the guard arrived and I returned to my seat. The entire altercation lasted about 30 seconds. The train halted at Tunbridge Wells, a police officer took our statements separately and informed me that my accuser didn’t want to press charges. Nor did I. He got off the train, I continued my journey and that was the end of it. Or so I thought.

A day later a British Transport Police officer rang my adversary — who turned out to be a university lecturer. For reasons I will never know, this call led to a change of heart by my accuser. The BTP subsequently interviewed me, and before I knew what had happened I was being accused of homophobic abuse and assault. I was stunned. I had allegedly interrupted the man’s attempts to make a phone call by asking him if he was ringing his gay lover.

This allegation could have ruined my life. Had I been found guilty, as a television critic and pundit who appears on the box and the radio regularly, my career would have been over.

The man had no evidence to support his claim. On my side, I had several witnesses who had heard nothing of the sort, plus CCTV footage that showed our altercation had been no more than an insignificant skirmish. Still, the police investigated my case with ardour. The investigating officers’ florid report to the CPS made it sound as if I’d beaten the hell out of the guy. It was nonsense. Nevertheless, charges were duly pressed.

During the long and stressful wait for my trial, it became clear to me that it wasn’t the non-assault they were interested in. It was the homophobic aspect that had mysteriously emerged 24 hours after the incident.

For the record, my accuser’s sexuality had never entered my mind and, it transpired, he wasn’t gay. But these allegations provided the British Transport Police with a potential opportunity to notch up an all-important statistic pointing to how wonderfully tough they are on hate crime. Zero tolerance. Every perceived slight is registered as a crime — even in cases such as mine where the evidence is based only on the accuser’s own account.

The court case itself, which happened last month, was a bizarre affair. The CCTV footage proved that I would have had no reason to interrupt my accuser’s call because he didn’t make one. Three gay friends took the day off work to assure the magistrates that I was not a homophobe. But the CPS’s prosecuting lawyer insisted that I was a hate criminal. The magistrates, in their wisdom, disagreed and concluded that I had acted in self-defence ‘with restraint’. My elation was tempered by the £15,000 I’d been forced to spend on hiring a legal team. I will be very lucky if I manage to reclaim a fraction of that sum.

I hope that what happened to me is rare. But somehow I doubt it. The director of public prosecutions Alison Saunders — who runs the CPS — has announced that new documents will soon be released to explain to a grateful public the definition of hate crime and to encourage everyone to go straight to the police.

Explaining why she wants to see more hate-crime offenders charged, Ms Saunders said: ‘We would like to see it higher because I do think that these cases are not reported enough.’ How can she know that? Is more than a thousand reports a week really too few? How many would suit her? Two thousand? Ten thousand? A million?

I cannot speak scientifically, but from my own experience I felt that I was in the grip of a kind of madness. Now that the pool of 1970s celebrities to arrest for historic sex crimes is running dry, the police and the CPS seem to have climbed aboard a new bandwagon.

The laws and guidance for prosecutors against homophobia, trans-phobia, racism and religious and disability prejudice are well-intentioned. But unless enforced with fairness and a sense of justice they represent a growing menace. Nottinghamshire Police have announced their intention to turn wolf-whistling into a misogynistic hate crime. Isn’t that just a tad over the top? Don’t coppers have better things to do?

For one year and eight months I had a ringside seat at the edge of insanity. A pathetic, tiny scuffle that I did not start escalated into a drawn-out legal battle. Hate crime. Be careful, it could happen to you.

Had I been found guilty, as a TV ­critic and pundit who appears on the box, my career would have been over

Kevin O’Sullivan was formerly television critic of the Sunday Mirror. He now runs the YouTheCritic website at TVKev.co.uk.