One of Zimbabwe's leading human rights campaigners has issued the world with a startling reminder of the horrific abuse and torture being suffered under Robert Mugabe's regime ahead of the country's elections in three weeks' time.

Takavafira Zhou, a trade union activist, was seized by government police two weeks ago and, while imprisoned, did not know if he would make it out of the torture chamber alive. Beaten to within an inch of his life, Mr Zhou was told to repeat the slogan "Robert Mugabe is always right", and now he has come to Britain to preach the reverse.

Still bearing the scars that are a testament to President Mugabe's brutal rule, Mr Zhou is to defy his oppressors by telling protesters today at the Action for Southern Africa (Actsa) pro-democracy rally in Trafalgar Square of the human rights violations taking place in his country. From there he and his trade union colleagues will go to Brussels to lobby the EU commissioner for Human Rights to take action against the dictator.

Download the new Independent Premium app Sharing the full story, not just the headlines

Mr Zhou says the time to act is now. "The suffering in Zimbabwe cannot continue for another day," he said, on arrival in London yesterday. "International leaders are complicit in human rights abuses in Zimbabwe by their failure to provide a solution or to induce a solution in Zimbabwe. We really wonder why Zimbabwe has taken so long to get international help. In Kenya it did not take so long. Why?"

Three weeks from today, Zimbabweans will be going to the polls, but Mr Zhou is not hopeful that the elections on 29 March will be democratic. "There will be no free and fair elections in Zimbabwe", he said. "And anyone who says there can be is daydreaming."

At the end of the month, the 84-year-old President will face two of his strongest opponents yet: his former finance minister Simba Makoni, 57, backed by ruling party rebels, and Morgan Tsvangirai, 55, the leader of the Movement for Democratic Change.

But many believe that even these strong candidates do not stand a chance against the closely guarded regime of Mr Mugabe and Zanu-PF. Outside electoral observers are being brought in, but opposition party members say that these will be taken entirely from countries that Mr Mugabe perceives as "friendly" to the regime.

Russia is the only European country to have been invited to monitor the elections while the majority of remaining observers will be from the Southern African Development Community (SADC) – a body which has already been criticised for dealing too leniently with Mr Mugabe.

Zimbabwe's Foreign Minister, Simbarashe Mumbengegwi, openly admitted yesterday that countries which had opposed Mr Mugabe would not be invited to monitor elections. "Clearly, those who believe that the only free and fair election is where the opposition wins, have been excluded since the ruling party, Zanu-PF, is poised to score yet another triumph," Mr Mumbengegwi said. But another Mugabe win would be far from a triumph for the Zimbabwean people, according to Lucia Matibenga, the vice-president of the Zimbabwe Congress of Trade Unions, and an electoral candidate for the MDC in Harare. She has also seen the catastrophic effects of Mr Mugabe's tight grip of power, and will stand alongside Mr Zhou in Trafalgar Square today.

"I don't see that we are preparing for free and fair elections given that violence is now institutionalised," said Ms Matibenga. "I think particularly in the rural areas people will find it very difficult to vote against Zanu-PF because of the threats made against them. Chiefs are paid by Robert Mugabe to use any means possible to ensure that their people vote for him."

Daily coronavirus briefing No hype, just the advice and analysis you need Enter your email address Continue Continue Please enter an email address Email address is invalid Fill out this field Email address is invalid Email already exists. Log in to update your newsletter preferences Register with your social account or click here to log in I would like to receive morning headlines Monday - Friday plus breaking news alerts by email Update newsletter preferences

For Mr Zhou, the reasons for a democratic challenge to Mr Mugabe are compelling. The 40-year-old university lecturer and president of the Progressive Teachers Union has witnessed first-hand how the President's clampdown on free speech has penalised innocent protesters.

Two weeks ago the human rights activist was leading a group of teachers handing out leaflets in Harare to campaign against the country's crippled education system when he was taken by Zanu-PF militia. The leafleting had taken place dangerously close to the party's headquarters, and within minutes of being discovered all the teachers were dragged into an underground cellar. Teams of 15 men used logs and iron bars to beat them. Mr Zhou and his fellow campaigners were battered – and some of the women sexually abused – with the iron rods, until they were left motionless on the blood-stained floor.

"It was so terrible. I've never seen such thuggery; I've never seen such brutality," said Mr Zhou. When the beatings became so bad that three of his fellow-protesters passed out, the police became afraid and took them to hospital, where they remained under police guard for four days.

Now the police are trying to charge them with criminal nuisance, but Mr Zhou says such a charge would be a gross injustice. "I don't see what is criminal or what is a nuisance about trying to save the collapsing education system", he said. Last month, he lost his job as a history lecturer at Great Zimbabwe University after submitting an anti-government paper. But Zimbabwe's universities have been closed anyway for several weeks now, as a jittery Mr Mugabe tightens his control on anti-government sentiment ahead of the elections.

When Mr Mugabe – a former school teacher himself – first became leader, there was hope that he would usher in a new era for education in Zimbabwe. But now, amid crippling inflation and government control, the schools lie empty and dilapidated; 25,000 teachers abandoned their posts last year, and a further 8,000 have left in this year already.

The few teachers who remain have been on strike since January over poor pay and the introduction of untrained militia as teaching staff. "This militarisation is what happened in Nazi Germany or with Mussolini's youth militia", warned Mr Zhou, who says that the teacher Mugabe of the 1960s would not have let such atrocities occur.

"The old Mugabe only wants his voice to be heard, but the young Mugabe wanted to hear the voices of the oppressed," he said. Teachers now have a salary of just four million Zimbabwean dollars, enough for little more than eight bottles of cooking oil. Mr Mugabe's soldiers, meanwhile are paid 2.3bn Zimbabwean dollars. "When Mugabe was 28, he said: 'If the government touch a cent of my salary I'll box them,'" said Mr Zhou. "We don't want to box Robert Mugabe; we're saying teachers have legitimate demands that should be met by the government."

It is unclear what horrors will await Mr Zhou on his return to Zimbabwe next week but he says he will not be gagged in his attempts to hold back the dictator's lust for power. "I am not afraid of going back," he said. "I take casualties as part of the struggle and part of leadership. Zimbabweans must note that they can't afford to stand on the touchline to watch a game they should be playing. Dictators do not willingly give up power, they need to be pushed."