One of the first essays I wrote as an undergraduate law student back in the 1980s was titled The Law is an Ass, Discuss. I hear my tutor repeating those lines every time I have to deal with a case of someone who has lived most if not all of their life in the UK, but is now facing deportation. These people can be shackled and rendered aboard a secretive charter flight out of the country. And this is entirely legal, in much the same way that the movement of millions of people across the Atlantic to be enslaved was legal in another time.

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Deportation flights often leave from UK military airbases but the human cargo for a flight bound for Ghana and Nigeria on Tuesday morning has been imprisoned at two Heathrow detention centres. Until a last-minute injunction on Monday, this human cargo was to include Kweku Adoboli. Kweku, who I represent, was convicted of illegally trading away £1.3bn at UBS investment bank in November 2012 and sentenced to seven years in prison. He was ordered to be deported to Ghana despite never having lived there as an adult. He has been granted his reprieve pending a judicial review. But at the heart of his story is Theresa May’s self-styled “hostile environment” towards immigration, which dates back to her time as home secretary.

In October 2010 a series of policy initiatives outlined in the Conservative party manifesto resulted in changes to the immigration rules. Non-EU partners of British people were kept apart based on earnings, appeals for family visits were removed and tough new rules on deportation were ushered in. The latter included a watering down of rights under article 8 of the European convention on human rights and automatic deportation for any non-UK citizen sentenced to more than 12 months in prison.

In 2013 the Home Office’s horrendous “Go Home” vans started patrolling areas with large non-white populations under the so-called Operation Vaken. In 2014, things got much worse as everyone from employers and landlords to banks and NHS staff were required to snoop on their staff, clients and patients. At the same time, safeguards given to the Windrush generation were removed, leading to the detention, deportation and in some cases deaths of British citizens.

Kweku was born in Ghana and left at the age of four because of his father’s employment in the Middle East. Aged 12, he was sent alone to boarding school in the UK and he has lived in Britain since. He has spent 26 of his 38 years in the UK, and 34 of them outside Ghana. The UK is the only country he knows; it is where he has built his life and formed his friendships and relationships, including with his partner, Alice. Kweku has already been punished, quite severely to my mind. It still seems odd to me that a relatively inexperienced young man was trading in such large sums.

But Kweku accepted his fate with dignity and since his release from prison in July 2015 has set about assisting other business managers to learn from his mistakes. Ironically the work he has been doing through the Forward Institute has included working with people from the Home Office and the army. Furthermore, he has been running workshops in schools and colleges and providing assistance to young entrepreneurs living challenging lives – he wanted to turn the lessons he has learned from his experience into something positive for the society and country that is his home.

It bears testament to who Kweku is that he got me to even look at his case when all his appeals were exhausted; that more than 130 cross-party MPs and MSPs wrote to the home secretary pleading for him to be allowed to remain in the UK, and that 75,000 people have signed a petition opposing his deportation. Yet Theresa May seems wedded to a policy of hostility on immigration and this is what has been informing Kweku’s treatment. She is expected to give a speech to the Conservative party conference in a couple of weeks in which she will signal even tougher controls, possibly to shift focus from her troubled leadership and Brexit difficulties.

But we’ve had enough. Does this great country really want to see people banished to countries they don’t know? Do we really want to see people who pose no threat to this country being punished twice? Isn’t the whole point of prison that it punishes and also rehabilitates? Stephen Shaw, the former prisons and probation ombudsman, said in his review of immigration detention last July that the practice of deporting people who had spent most of their lives in the UK should end, and he is right.

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There is a presumption enshrined in law that the public interest requires the automatic deportation of individuals sentenced to longer than four years, unless this would be a breach of the ECHR or the UN refugee convention. It is also the case that there must be compelling reasons to override the public interest. But if that public interest is immutable how can this be compatible with human rights legislation? If the requirement for removal can be increased with aggravating factors, surely it should be reduced where there are compelling considerations. Rarely have I seen a case with such compelling mitigating factors as Kweku’s. But his deportation was sanctioned in the public interest, though whose public interest remains unclear.

Ironically, it is likely that the Ghanaian- and Nigerian-born men and women aboard Tuesday’s flight to west Africa will have parents or grandparents who were British at birth when those countries were colonies. Both countries feature in the top five of the birthplaces of people helped through the Windrush scheme. This links Kweku and many of those who will be deported this week with the “hostile environment” policy that led to the scandalous treatment of the Windrush victims.

• Jacqueline McKenzie is the lawyer for Kweku Adoboli