The disclosures, which last night plunged the Government into a new row about its controversial policy, highlight the grave danger that deportees face when refused asylum and forcibly deported back to the country ruled by President Mugabe's regime.
The cases uncovered by the IoS include at least six incidents of refugees being assaulted; one beaten so severely he was hospitalised; one being nearly drowned during interrogation; and others dumped without food and water deep in the bush.
These new revelations will fuel the bitter row now enveloping the Home Secretary, Charles Clarke, after he refused to halt the forcible returns of failed Zimbabwean asylum seekers despite the violent repression now gripping the country.
Kate Hoey, the Labour MP and former minister, said these cases meant it was "shockingly wrong for the Home Office to continue to deport people". Ms Hoey added: "Charles Clarke keeps saying that we have no proof but I met people when I was there who had been tortured. Anyone who is deported back from the UK, even if they are not a political activist, is at risk because the anti-British feeling is so strong."
Ministers are planning a fresh round of deportations this week as they face a series of legal challenges over the continued detention of these refugees, and allegations of ill-treatment by guards at detention centres. The Government dramatically lost one case last night after the High Court blocked attempts to deport a 26-year-old woman on the grounds that her deportation was "inappropriate".
Menzies Campbell, deputy leader of the Liberal Democrats, said last night the evidence uncovered meant the Home Office now had a moral duty to suspend all deportations to Zimbabwe. David Davis, the shadow Home Secretary, asked that the Government suspend deportations until a rigorous method of monitoring the safety of those returned to Zimbabwe could be put in place.
The controversy erupted last month after scores of Zimbabwean asylum-seekers in immigration detention centres around the country began hunger strikes in protest at Home Office plans to deport them. Up to 125 detainees are now refusing food.
The allegations uncovered by the IoS - based on investigations by Zimbabwean human rights groups and church leaders - include:
* A refugee in his 40s sent back last December alleges he was handcuffed at Harare airport by Zimbabwean secret police and driven into the bush. He was then beaten repeatedly, had his head forced into a bucket of water and was accused of being a British spy.
* Also in December, a refugee was seized a day after being interrogated for three hours at Harare airport and beaten so badly he had to be rushed to hospital. It is believed his assailants were militia linked to the ruling Zanu-PF regime.
* In May, British officials escorting another man back to Zimbabwe allegedly handed him straight to the secret police at Harare airport. He was assaulted by his interrogators, and is now in hiding.
* Last month, another returnee was interrogated at the airport, made to divulge addresses of other dissidents, then arrested at his home and interrogated again.
Dr Brighton Chireka, director of the Zimbabwe Association, said the regime's secret police, the Central Intelligence Organisation, who are increasingly paranoid, only focused on people they believed were dissidents or spies. "The Central Intelligence Organisation is the most feared in Africa," he said. In other cases, suspected dissidents are seized by militias, linked to Zanu-PF, whose favourite techniques include forcing metal rods through the victim's armpits and using paddles studded with roofing nails to beat people with.
The fate of the Zimbabweans who have been expelled by the Home Office is now being investigated by human rights activists, lawyers and religious groups.
Evidence compiled by the Zimbabwe Human Rights Group, the Zimbabwe Association and a Methodist preacher from the Midlands, Dr Martine Stemerick, suggests there could be at least 10 cases of refugees being persecuted.
Dr Stemerick has recently returned from a three-week-long trip to Zimbabwe, covertly recording evidence about the ill-treatment of returned asylum seekers.
However, tracking deported refugees in Zimbabwe is fraught with difficulty. Expatriate leaders say many asylum-seekers go into hiding immediately after they return, or are too fearful of retaliation to co-operate with lawyers and opposition groups.
Susan Harland of the Zimbabwe Association, said: "It is incredibly frustrating. These people don't have the confidence to make statements because they fear their names will be plastered everywhere. If they did, we'd be able to stop these deportations happening."
The ban on deportations to Zimbabwe was lifted in November as officials said there had been a substantial rise in the number of people making asylum claims falsely saying they were Zimbabwean. Since January at least 95 people have returned to Zimbabwe, a figure that includes people who left voluntarily.
Next week, lawyers are preparing a High Court challenge over Mr Clarke's refusal to release Crispen Kulinji, the most prominent hunger striker and opposition activist. Human rights groups are investigating reports that at least two male hunger strikers in Harmondsworth were placed in solitary confinement by guards as punishment for leading the protest. A third man is also understood to have been placed under "room arrest".