In August 1997, Mohamed Al Fayed phoned my late father, George Carman, QC, to arrange a joint meeting with Diana, Princess of Wales and his son Dodi. George’s advice was needed on privacy matters. The meeting never happened. On August 31 the Princess and Dodi were killed, together with driver Henri Paul, when their Mercedes crashed in the Pont de l’Alma tunnel.

At the British inquest into their deaths, to be opened today by the coroner Lord Justice Scott Baker, the jury will be visiting the site in Paris. The inquest could last until next Easter.

Al Fayed will be represented by Michael Mansfield, QC, a name synonymous with fighting miscarriages of justice. Among his many causes célè-bres are the family of murdered black teenager Stephen Lawrence and Angela Canning, wrongly convicted for murdering her two sons.

Mansfield, 65, wears many labels: human rights champion, bike-riding vegetarian and radical socialist, albeit with a touch of champagne dampening the edges. He has even written a novel called, appropriately, The Inquest. Among journalists, colourful is the epithet most often applied to the twice-married father of six. And whereas most lawyers see their role as providing dispassionate counsel, he embraces passion with a capital P. “Of course I get emotionally involved in my work,” he says. “It’s not like being a surgeon: just another body that comes along, cut ’em up and on to the next. I can’t do that. I identify with the individual client, understand how they tick in order to communicate that to a jury. By the end of a case, when you’ve lived with somebody for a period of time, you identify with them. The emotional involvement stays with you.” One client who remains a good friend is Arthur Scargill, the former NUM President.

Quite how Mansfield relates emotionally to Al Fayed is unknown, although both are clearly sceptical of establishment thinking. Given Mansfield’s strongly declared republicanism, the two men would seem to be further united by their mutual opposition to the Royal Family. But we will have to wait and see whether he advocates at the inquest his client’s repeated claim that the Duke of Edinburgh is “a racist who orchestrated Diana’s murder”. Al Fayed has also called for the Prince of Wales and the Duke to give evidence, maintaining that the Princess and his son were murdered as part of a plot by the British Establishment.

When Mansfield was invited to become a judge – more than a decade ago – he turned it down without hesitation: “I’d be interfering, intervening and never shut up,” he quips. “More importantly, I thought the work that I do inside and outside court – campaigns, political activity and so on – would suffer.” He adds that “English judges have improved enormously. We live in a very interesting period. I never thought I’d see the day when the judiciary in the House of Lords is the protector against the politicians.”

Mansfield set out his stall as a defender early on. His reputation was forged when he defended a leader of the Angry Brigade, an anarchist group that bombed several ministerial homes. “Because the State employed top-level people, I thought I would like to provide a counterbalance – to help people who might not otherwise have a voice,” he says. “Everybody saw me as a red under the bed purely because I was anxious to do that kind of work.”

He provokes strong reactions from colleagues. According to one leading criminal silk, “he’s arrogant, very full of his own self-importance”. Another says that “he’s a hero to many and an inspiration to a generation of young barristers”. By his own admission, success has taken his earnings to £300,000 a year.

That makes him “a millionaire campaigning leftwinger”, and “Moneybags Mansfield” in the eyes of the tabloids. “It’s the sort of cheap abuse I ignore,” he says. “If you’re a public figure, then you don’t rise to it. I come from a very modest background and I didn’t come into the law because it’s well paid. I didn’t think: this is a goldmine for me. What I find really rewarding is when the public come up to me – nearly every day – and say: ‘Keep going.’ If that’s all that ever happens, that’s fine by me. I’m not interested in honours.” Experience has taught him to be circumspect about the prospects of any case and always to keep an open mind. “I learnt the hard way that I’m not the arbiter of truth. I may have a view which might be totally wrong.

“Having had so many juries who disagree with my view one way or the other – convicted when I thought they should acquit or the other way round – I’ve stopped making that judgment. But I do find it very upsetting when I lose.” Quite what winning and losing means in the context of this inquest remains to be seen.

Explore Law

• Columnists

• Law Panel

• Law Reports

• Student Law

Times Recommends

• BGC 'set aside £40m to lure Tullett brokers'
• Legal aid review to ensure value
• Fears as 21 magistrates' courts face closure