When Gordon Brown condemns the Zimbabwean tyrant Robert Mugabe I can't take him seriously. He's all talk, no action. I had Mugabe under citizen's arrest in London in 1999, but the Government allowed him to return to Zimbabwe to continue his murder and mayhem.

If Mugabe had been put on trial in 1999, Zimbabwe would have been spared the past nine years of torture, rape, kidnapping, murder, rigged elections, hunger and now disease. Tens of thousands of lives might have been saved.

Labour funked the opportunity to prevent this terror. It failed to prosecute a leader who, a decade ago, was already guilty of crimes under international humanitarian law.

While I applaud Archbishops Desmond Tutu and John Sentamu when they call for Mugabe to be indicted, why didn't they urge this in the late 1990s? The Zimbabwean dictator's human rights abuses were evident by then. He had massacred 20,000 civilians in the Matabeleland region of Zimbabwe during the 1980s in a Stalinist-style purge designed to crush support for his rival nationalist leader, Joshua Nkomo.

It was hearing about these massacres that fired me up to do something to support the brave Zimbabweans who were resisting Mugabe's despotism. I was appalled that the international community had ignored the Matabeleland slaughter and was doing business as usual with the Mugabe regime.

The 20,000 murders in Matabeleland were the equivalent of a Sharpeville massacre every day for more than nine months. Since then, the killing fields of Zimbabwe have continued to flow with blood. Mugabe has murdered more black Africans than even the apartheid regime in white-ruled South Africa. A liberation hero turned despot, he is Ian Smith with a black face - only many times worse.

I was shocked that liberals and leftwingers who had campaigned so honourably against apartheid were silent. They were outraged by a white racist regime killing black people, but not when the killing was being done by a black tyrant. This double standard and indifference to mass murder appalled me.

My determination to act was compounded when, in 1999, two respected black Zimbabwean journalists, Ray Choto and Mark Chavunduka, were arrested and tortured. According to Amnesty International: “Military interrogators beat both men all over their bodies with fists, wooden planks and rubber sticks, particularly on the soles of their feet, and gave them electric shocks all over the body, including the genitals. The men were also subjected to ‘the submarine' - having their heads wrapped in plastic bags and submerged in a water tank until they suffocated.”

Choto and Chavunduka's interrogators told them they were being tortured on Mugabe's orders. The President subsequently refused to condemn their torture and publicly stated that they deserved it.

Since governments were refusing to bring Mugabe to justice, I decided to have a go. My plan was to make a citizen's arrest of President Mugabe on charges of torture, with the affidavits of Choto and Chavunduka as evidence.

The first attempt was in late 1999, when Mugabe came to London on a private shopping spree. As the President's limousine left his hotel, by pre-arranged plan, my three OutRage! co-conspirators - Alistair Williams, Chris Morris and John Hunt - ran into the road, forcing it to halt. I ran from behind, opened the rear door, grabbed Mugabe by the arm, and read him the charge: “President Mugabe, you are under arrest on charges of torture.” Mugabe's jaw dropped. His face was contorted with fear. I thought to myself: now you know how your victims feel, except we aren't going to kill you.

I then phoned the police. When they arrived, officers ripped the Amnesty International dossier from my hands, arrested us and gave Mugabe a police escort to go Christmas shopping at Harrods. We were held in the cells at Belgravia police station for nearly seven hours until the Government and police stitched up a deal to let Mugabe return to Zimbabwe, where he resumed his assaults on democracy and human rights.

My second attempted citizen's arrest was in Brussels in 2001, when I ambushed Mugabe in the lobby of the Hilton Hotel. This time his bodyguards were ready for me. I was beaten unconscious. At one level, this was a good thing, because TV film of the beating helped to alert the world to Mugabe's brutality.

I was left with chipped teeth, and this week I was at the dentist again having more treatment to repair the damage. The beating has also affected my eyesight, memory, concentration, balance and co-ordination. I can still cope, but I am a bit slower than I used to be. These injuries are, however, nothing compared with the terrible tortures inflicted on Mugabe's critics inside Zimbabwe.

Some people say that my attempt to arrest Mugabe was brave. Not so. Real bravery is the courage of Zimbabweans who defy police whips, tear gas and bullets.

My questions to Gordon Brown are the same as I put to Tony Blair in 1999: what is the point of having human rights laws if tyrants like Mugabe can violate them with impunity? How many people does he have to kill and torture before he is bought to justice? If Slobodan Milosevic can be indicted and put on trial, why can't Robert Mugabe?

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