I know how they feel, those women who are considering suing the police over the sexual behaviour of environmental spy Mark Kennedy. About 20 years ago I had, er, relations with a man who turned out to be an informer for the apartheid government in South Africa. I was in my early 20s, a student at the University of the Witwatersrand in Johannesburg, and deeply involved in the anti-apartheid movement. We all knew the left had been infiltrated by agents of the state, but I was small fry and never imagined they would pay any attention to me.

The spy's name was John (or so he said), and he lived in a communal house down the road from mine in the shabby suburb of Berea. It was after one of those long meals of lentils and carrot stew washed down with cheap South African red wine that our romance blossomed. I remember evenings spent discussing the role of the vanguard in struggle politics and the re-education camps we planned for the enemy after liberation. The relationship didn't last and he disappeared a while later, but it was some years before I heard he had been an informer. I was left feeling rather grubby, and rueing my taste in men. Yet I never thought that he had specifically targeted me, or that anything I said had been of particular use to his police handlers.

A far greater betrayal came in the form of Joy Harnden, another spy in my organisation, the End Conscription Campaign. We weren't particularly close but I remember being impressed by her dedication and intimate knowledge of the workings of the apartheid state. (Odd that.) I recall one conversation when she pumped me for personal information about a housemate who had recently been released from police detention. I should have noticed something was amiss, but I admired Joy and was pleased to spend time with her.

I later learned that she was a lieutenant in the security police and was responsible for the death of at least one ANC comrade. It still makes me feel sick. She changed her name and lived in Scotland for a while, and sometimes I fantasise about tracking her down and confronting her.

But it didn't cross my mind to take legal action against the police over any of this. After all, it was South Africa in the 1980s and we were trying to overthrow the state. We expected it. But it's not what I would expect if I was protesting against climate change in Britain today.