A chartered plane, PTV030, is due to take off at 15.30 from an undisclosed London airport and fly direct to Colombo. Human-rights organisations have called on the UK Border Agency to halt the flight on the grounds that Tamils who are known to be critical of the Sri Lankan government have been brutally treated following their return.

The forced removals come as Mahinda Rajapaksa, who was the architect of Sri Lanka's final victorious push three years ago against the Tamil Tigers – a military offensive which defeated the brutal insurgency group but also led to the deaths of tens of thousands of civilians – flies into the UK to join the Queen's Diamond Jubilee celebrations.

Human Rights Watch has documented 13 credible cases over the past two years in which failed Tamil asylum-seekers from Europe have been tortured after landing in Sri Lanka, and warns that those cases are likely to be "just the tip of the iceberg".

Mr Rajapaksa's government has been accused of committing war crimes during the military offensive and of continuing to preside over a culture of impunity in which kidnap, extra-judicial killings and torture are still commonplace, particularly in the heavily militarised Tamil areas in the north.

The Foreign Office's latest report on human rights describes Sri Lanka as an area of "serious concern" when it came to abuses. But that has not stopped the UK Border Agency, which is under political pressure from the Government to ramp up deportations, from forcibly removing hundreds of Tamils in recent months.

The agency is notoriously secretive when it comes to forcible removals, rarely announcing them until the very last minute and providing few details about who is on board.

There have been at least four chartered planes in the last six months delivering Tamils back to Sri Lanka.

Some of those on board today's flight include people who have overstayed their visa and immigrants who have been convicted of a criminal offence. But it also contains dozens of ethnic Tamils who have had asylum bids turned down and are at risk of political persecution.

The Independent yesterday spoke to one Tamil man in his mid-twenties who is currently being held in Yarl's Wood detention centre and is due to be on today's flight. He said there were six people on his wing who were failed asylum-seekers who thought they would be at risk of torture or worse if they were returned. "Everybody is crying," he said. "We all know about cases where people have been tortured or killed after they were returned. Why is the UK government doing this?"

The man, who requested his identity remain anonymous for fear of reprisals if he is removed, said he travelled from Jaffna to Britain in 2006 to escape the violence that had plagued northern Sri Lanka for three decades. He added that both he and some of his fellow deportees played prominent roles in recent protests in London against the Sri Lankan government.

"Whenever there were demonstrations the Sri Lankans would send people down to photograph the protesters," he said. "They know exactly who we are. That's what scares us."

The UK Government insists that those who are forcibly removed are individually assessed to make sure that they are not at risk of torture on their return. But Human Rights Watch says they have at least three cases of Tamils who had been forcibly removed from the UK and subsequently tortured.

"There are likely to be many more cases, because these are the people who have managed to find their way from Sri Lanka to the UK, and that we have managed to interview," said David Mepham, director of HRW UK.

"The UK should suspend the forcible removal of Tamil asylum-seekers pending a review of its processes for assessing asylum claims by Tamils."

A UK Border Agency spokesman said: "The UK has a proud record of offering sanctuary to those who need it, but people who do not have a genuine need for our protection must return to their home country.

"We only undertake returns to Sri Lanka when we are satisfied that the individual has no international protection needs. The European Court of Human Rights has ruled not all Tamil asylum-seekers require protection."

Tamil returnees are raped, whipped and burned

Suthan knows all too well how hollow assurances that Tamils deported back to Sri Lanka are safe can be. He first fled to the UK five years ago after the Sri Lankan Terrorist Investigations Department accused him of having links to the Tamil Tigers.

During his asylum application he presented medical evidence showing that he had been beaten with sticks and burned with cigarettes but his request was turned down.

Last year he was placed on a chartered flight and returned to Colombo. He was questioned on his arrival at the airport in the presence of an official from the British High Commission and was later released.

But the interrogations continued. After trying to return home he was picked up by security officials and claims he was tortured, including being whipped with electric flex, burned with cigarettes and having his head immersed in a bag filled with petrol.

After paying a bribe he escaped to the UK again and is now represented by Freedom from Torture, which has used medical evidence to document numerous instances of deportees being brutalised on their return to Sri Lanka.

"This situation has gone on long enough," says Keith Best, Freedom from Torture's chief executive. "Forcible returns of refused Tamil asylum-seekers must be halted until the UK Government is sure that they will not be delivering people into the hands of their torturers."

Even the asylum panels have recognised that torture continues despite the end of Sri Lanka's civil war. In late 2010 the Immigration and Asylum Chamber accepted that a Tamil woman who had been returned to Sri Lanka by the UK authorities was tortured and raped. A second 33-year-old man was also granted asylum last year after a tribunal accepted that he had been beaten and burned with hot metal sticks after his return.

Nonetheless the British Government has stepped up deportations.

Jerome Taylor

Suthan's name has been changed to protect his identity