"This isn't a sob story," says Fieldfisher regulatory head and Brexit taskforce chief John Cassels. But, having endured at the brink of personal catastrophe, his is not your familiar tale of City success.

Sitting down with Legal Week, he describes a life shaped by family tragedy, the struggles he encountered as a young gay man growing up in Scotland and, as a lawyer, the uneasy tension between winning business and calling out discrimination.

Coming from a family line of "dirt-poor blacksmiths and farmers" in the southern Scottish town of Kilmarnock, Cassels learnt very early on to deal with tragedy when his mother died after a six-year battle with Leukemia. He was 12.

Affected by her death, his father became "emotionally absent".

"My father was extremely homophobic as a result of his own upbringing," he said. "It made me question who I was – it kills your self-esteem."

He called it unnatural, he said I was worse than a criminal and that he never wanted to see me again

Cassels felt forced to conceal his homosexuality from his father. And school, where he was bullied regularly, provided little respite. The impossibility of living in such an environment meant that Cassels left home at 16. But he still attained good grades at school. He went on to study law at Glasgow University and despite leaving then returning sometime later, eventually graduated with a first-class honours degree.

It was at this stage he felt bold enough to visit his father and finally come out to him.

"I went to him and, the moment came. I just said it – 'dad, you know I'm gay, right'. It felt like the world had stopped."

The response was predictably hostile.

"He called it unnatural, he said I was worse than a criminal and that he never wanted to see me again."

London law, private pain

He moved to London to embark on his legal career, starting at magic circle firm Slaughter and May where he spent four years. He then joined US firm Shearman & Sterling where over three years he continued to develop his competition law specialism.

Life, it seemed, was looking up. His career was taking off. He was in a loving relationship. He wrote to his father every three months telling him he still loved him and that he wanted to see him. But tragedy was to make a pernicious return.

It was strange – working in the outwardly privileged world of the City, and returning home in the evenings to see wrapped packets of tin foil around the flat

His boyfriend at the time developed a heroin addiction. Then, 18 months into their relationship, he suddenly collapsed and died in the middle of the street.

"It was a very dark time," says Cassels. "It was strange – working in the outwardly privileged world of the City, and returning home in the evenings to see wrapped packets of tin foil around the flat. Witnessing him on drugs, in withdrawal – have you ever seen something like that?"

Cassels talks about how often it felt the pain was too great to bear.

But then, one day, after two and a half years writing to his father to no reply – he received a letter. It was his father telling him he was "really sorry", and that he "wanted to see him again".

Cassels says: "We now enjoy a close and supportive relationship. His change is testament to an openness and willingness in people to see things differently."

Calling out clients

In his career, Cassels' experience with colleagues and clients has not always been straightforward either. He laments an episode in which another lawyer made an assumption about his interests outside of work because he was gay. He feels it is necessary to call people out, whether a partner or otherwise, on homophobic behaviour, even if words are uttered in otherwise genial settings.

But when it comes to dealing with clients, he admits, the situation becomes that bit more complex, and one in which black-and-white answers are not readily available.

You're trying to build a relationship, but you don't know what their views are. There is a huge fear of rejection

He discusses the tension between calling out homophobic behaviours and the pressure to win business as a partner. He talks in particular about a nervousness he felt when clients in the past asked questions like, 'are you married?'.

"You win work by fostering relationships built on trust – and you do that by being open. But I haven't always been able to be forthcoming with some clients. You're trying to build a relationship, but you don't know what their views are. There is a huge fear of rejection."

He adds: "In some cultures and jurisdictions, the answers are rarely straightforward and it is, admittedly, difficult to call out client discrimination."

He agrees that more needs to be done in this regard, and that calling out even apparently perfunctory remarks is the only way workplace discrimination can be tackled.

The issue exists despite plenty of progress within private practice firms on LGBT issues. A number of City firms were this week included in equal rights charity Stonewall's annual top 100 list of employers, which lists the UK companies that work hardest to achieve equality for LGBT people.

But Cassels also believes his experiences have helped him in his decisions at work, and helped him to build better relationships with both his juniors and fellow partners.

"These experiences determine how you interact with people," he says. "Team meetings, for example, can become a forum for partners to gloat about their achievements. But we have a meeting each week where associates, paralegals and more senior lawyers are encouraged not to simply report on what they're working on. I encourage everyone to take their moment and to communicate with consciousness."

And all things considered, Cassels regards himself lucky, as these experiences have lent him an "external softness and an inner strength – unlike the reverse, which we see too much of in the City".