Senthooran Kanagasingham, 35, admits manslaughter of friend Sonia Burgess, 63, on grounds of diminished responsibility

A 35-year-old man who deliberately pushed a renowned immigration lawyer to her death under a London tube train has been jailed for life.

An Old Bailey jury cleared Senthooran Kanagasingham of murder. But he admitted manslaughter on the grounds of diminished responsibility and was jailed after the court was told that doctors believed he no longer required hospital treatment for paranoid schizophrenia.

At the time of the attack during the evening rush hour at King's Cross station in October last year, Kanagasingham had been undergoing gender reassignment surgery and was known as Nina. But during the trial he said he wished to be referred to as a man and by his male name.

Kanagasingham's victim was 63-year-old Sonia Burgess, who lived as a woman with family and friends but was known in professional life as David Burgess, one of the UK's most celebrated immigration lawyers, responsible for landmark judgments in the House of Lords and the European court of human rights.

The court heard Burgess had befriended Kanagasingham and offered her support and financial help, despite worries about her mental state. Kanagasingham wanted to undergo a gender realignment, which her family in Sri Lanka opposed. The pair were returning from seeing Kanagasingham's GP in Cricklewood, north London, when she pushed Burgess under a Piccadilly line train. A note in Kanagasingham's rucksack said she was "broke, depressed and suffering from gender dysphoria".

Brian Altman QC, prosecuting, said that witnesses saw Kanagasingham push Burgess "very hard" with both hands in the middle of the back. CCTV footage showed her bend her knee to gain maximum force. He said: "The push was entirely deliberate and it was executed with the intention of killing Sonia Burgess. After all it could hardly have been done with any lesser intention than to send Sonia to her death. It was born of anger and malice."

Telling Kanagasingham he should serve a minimum of seven years in jail, Judge Stephen Kramer said Burgess had been "a really good and generous friend to you".

Kramer said: "It's clear by your act you have deprived a family of a much loved father and the community of a very giving person as well as a highly respected and distinguished professional. You formed an attachment to Sonia in which you became needy and relied on her. If you were again to form a needy attachment as you did to Sonia, you would in my judgment be a real danger to such a person."

Edward Rees QC, defending, said Kanagasingham was not eligible for a place in a secure hospital and would receive treatment in jail.

In his life as David Burgess, Altman told the court, the solicitor had established "an enviable and brilliant reputation" in human rights and immigration law, firstly with his own law firm and then with another firm in Wood Green, north London.

But away from work Burgess lived almost entirely as a woman and was known to family and friends as Sonia. Sonia was "gender-variant", Altman said, and did not wish to have surgery. "Sonia was caring and generous with her time. She was tolerant of others and she habitually helped others with their problems."

Burgess's family said they had no wish for retribution. "This was not what our father wanted," her daughter, Dechen Burgess, told the court. "She was trying to help Nina. Ideally we would like Nina to recognise the harm she has done to many lives, but we hope she can one day reach such a place so she can live life in fullness as our father would have wanted."

Watched by her younger sister, Kusang and brother, Tenzin, Dechen said: "We miss the possibility of being able to watch Dad evolve into the person that she wanted to be, much that had eluded her for much of her life because of work commitments. One of the great sadness is the thought of missing the opportunity of sharing of future children with her, she would have made a great grandparent."