The British government is forcibly deporting asylum seekers who are then tortured in Sri Lanka, according to the testimony of one victim who was left scarred and suicidal after a brutal two-week ordeal.

The victim told the Guardian he was tortured over the space of 17 days after being deported from the UK last year. His torturers accused him of passing on to British officials information about previous beatings at the hands of state officials and other human rights abuses, to ruin diplomatic relations between the two countries.

The revelations come as Sri Lanka's head of state, Mahinda Rajapaksa, is expected to have lunch with the Queen and other heads of Commonwealth states as part of jubilee celebrations on Wednesday. The coalition is coming under increasing pressure to revisit its policy, which suggests it is safe to return Tamils to Sri Lanka. Last week the high court halted the deportation of 40 people to the island at the last minute, citing human rights concerns.

In an in-depth interview, the former member of the rebel Tamil Tigers' intelligence service said he was tortured after the Home Office deported him and two dozen other asylum seekers in June 2011. More than 70 UK border guards accompanied girls and men on the flight from Stansted airport last summer after a last-minute judicial review and his initial claim for asylum based on previous evidence of torture, were turned down by UK authorities, he said.

Speaking through a translator, the victim, who wants to be identified only as Hari for fear of further retribution by Sri Lankan authorities, said that six months after he was deported, security personnel arrested him and beat him with rods, put petrol-filled plastic bags over his face and hung him by his feet with a nylon rope. Hari's back displays a welter of scars and the Guardian has seen medical reports supporting his claims.

Hari managed to bribe his jailers and escape back to the UK via Russia and is now filing a second claim for asylum. "I came here with a hope," he said. "I believed that the UK authorities would consider my case reasonably but, regardless of all my history and the evidence, they sent me back and I had to suffer again."

Last week, the UK government forcibly deported several other Sri Lankans, ignoring pleas from human rights organisations to halt flights in the face of mounting evidence that UK and European returnees have been tortured.

The Home Office has insisted it is safe to return Tamils to Sri Lanka after the end of a long civil war and quotes a European court ruling that "not all Tamil asylum seekers require protection". However, officials are facing increasing pressure to change their policy.

In a dramatic turn of events, a senior high court judge last week halted up to 40 deportations from taking place as the plane waited on the tarmac.

Citing evidence from Human Rights Watch that returnees were being tortured on arrival, the judgment granted a last-minute reprieve. Drafted by Justice Eady and seen by Channel 4 News, it is reported to have said: "The recent Human Rights Watch report, dated 29.05.2012 suggests that there may be new evidence relevant to the risk of ill treatment."

Human Rights Watch said that in one of the 13 cases it had taken up, the UK's immigration and asylum chamber had accepted that a woman who managed to make her way back to the UK in late 2010 after having been deported by Border Agency staff was tortured and raped on her forcible return to Sri Lanka.

A spokesman for the British Tamils Forum said the Human Rights Watch cases were likely to be "just the tip of the iceberg".

"Sri Lanka's human rights record is appalling," the spokesman said. "People fear for their lives when deported back to Sri Lanka. If the British government can't guarantee the deportees' safety after deportation, all removals of failed asylum seekers must stop immediately."

Commenting on Rajapaksa's UK visit, Charu Hogg, associate fellow at the thinktank Chatham House and a former Human Rights Watch researcher, said: "The Sri Lankan Tamil community in the UK and elsewhere is extremely aggrieved over the conduct of the Sri Lankan government in the last phases of the conflict in 2009.

"Rajapaksa technically leads the Sri Lankan armed forces and is responsible for the conduct of his troops. In the eyes of many UK Tamils he is ultimately accountable for numerous violations of human rights and international humanitarian law committed by his troops."

In a statement, a UK Border Agency spokesperson 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 that not all Tamil asylum seekers require protection."