Michael Mansfield’s autobiography is called Memoirs of a Radical Lawyer. For many, the juxtaposition of the two words “radical” and “lawyer” is a contradiction in terms, possibly, even a bit of a joke. But if anyone can carry off that tricky 1960s label, then Mansfield can.

So what — if anything — does it mean to be a radical lawyer? “For me, it means going back to first principles,” says the QC, referencing the word’s Latin origin radix meaning roots. “It is about being able to strip away the paraphernalia that encumbers topics of discussion where people have superimposed their own predilections and prejudices. You have to strip that away and get back to first principles.”

The contents pages of Mansfield’s book is a fairly comprehensive list of left-wing causes célèbres over three decades (miners’ strike, Birmingham Six, Stephen Lawrence, Jean Charles de Menezes ... ). But the longstanding president of the Haldane Society of Socialist Lawyers insists that “you can be a radical on the right wing as well as on the left. It’s much more about an intellectual process.”

Mansfield was one of a generation of lawyers who joined the profession in the late 1960s or early 1970s with a conviction that they could use law to change society fuelled by far-left politics and the US civil rights movement. Those young radicals went on to become leading members of the Bar including Helena Kennedy, QC (or Baroness Kennedy of the Shaws, as she is now), the former Communist Party member Stephen Sedley (Lord Justice Sedley), as well as solicitors such as Sir Geoffrey Bindman, Louise Christian and Patrick Allen.

To say there was a generational clash between the upstarts and a deeply conservative profession is to put it at its mildest. “I frequently used to hear vile, unprintable, almost hysterical remarks made about leftie lawyers,” wrote Marcel Berlins, the legal commentator, in a New Statesman article in 1999. “I have seen judges in court barely able to speak civilly to the likes of Michael Mansfield, such was their hatred of him and the threat they thought he represented to the good order of the law.”

The hostility “through the 1970s and 1980s and possibly into the 1990s” has since “evaporated”, Mansfield reports. So complete has the change been that the silk claims that there now exists “an abiding respect for those that stood for those kind of principles, even if they hadn’t been appreciated at the time. I hope I’m not overstating that.”

Have the radicals sold out? “There aren’t many of us left,” Bindman reflects. “There has been an increasing polarisation within the profession between those who work for individuals who are deprived or vulnerable and those in the commercial sector who have become on the whole very, very rich.” In 1974 he started his firm, now one of the largest legal aid firms in the country, inspired by his experiences volunteering at a Citizens Advice Bureau and working in Chicago for the former presidential candidate Adlai Stevenson’s law firm.

“We’re absolutely true to our roots. That is what keeps us going,” insists Patrick Allen. He set up Hodge Jones & Allen three years later with Peter Jones and Henry Hodge, His “moment of conversion” came at a student demonstration against a visit by the South Vietnamese Ambassador, at the invitation of the right-wing Monday club, at the University of Oxford. A friend was arrested on trumped-up charges and Sir Stephen Tumim, who later became a reforming prisons inspector, got him off. “That changed the whole idea what it was to be a lawyer,” Allen says. His firm is acting for G20 protesters arrested on April 1 on what the firm insists are “joke” charges.

Bindman reckons his firm’s vision remains true “but because of the decline of legal aid the proportion of the publicly funded to private work has changed”. He says that many of his “radical” colleagues have left cutting-edge law for more lucrative areas “running equal-pay claims in the North of England or environmental work and clinical negligence work on large-scale, no win, no fee basis. Some have become quite prosperous.”

The suggestion that legal radicalism may be a thing of the past elicits a heartfelt groan from Roger Smith, director of Justice. “There are a number of baby-boomers who came into the profession in the 1970s, now retiring and feeling old and crabby.” They went through “the heyday of legal aid and frankly made a lot of money”. “Many were able to wear their hearts on their sleeves and keep a full wallet in their back pocket. The grumpy old men should shut up and take their pension.”

Does the label “radical law” have currency today? “The world has changed and the political ideology has changed,” Smith argues. “Where is the radical Left more generally?” He points to the enthusiasm of young lawyers campaigning on any number of disparate causes from “human trafficking, to green issues and environmental issues”.

Laura Janes, as a founder of the Young Legal Aid Lawyers, agrees. “Everyone knows who everyone else is but we’re not selling ourselves as ‘radical lawyers’,” says Janes, a solicitor at the Howard League for Penal Reform. “We’re Thatcher’s babies. We weren’t brought up to have an overtly political view.”

Many of her peers feel bogged down by what Janes calls the money question — the difficulties that have beset legal aid. “It seems to me one of the problems of being a young radical lawyer is that you are constantly fighting for the right to be able to fight.”

Kennedy argued recently that the radical lawyers did not sell out and did not change their views “but society moved towards them”. “The causes we took up — discrimination, racism, sexism, homosexual rights — have entered the mainstream. People in the legal profession who shared our views have gone on to become judges.”

And Mansfield argues that the forces of conservatism are the politicians, not the lawyers. He flags up the 2004 Belmarsh ruling by the law lords (that the indefinite detention of foreign terrorist suspects was incompatible with the Human Rights Act 1998) as an example of contemporary judicial radicalism. He says: “Over the past decade the most regressive and reactionary force in the country has been the politicians.”

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