Anyone who had never heard of Philip Gould  which would mean, I'd guess, more than 90% of the population outside Westminster  will have wondered why his final illness and death last year at 61 were considered so newsworthy. The long obituaries and tributes were preceded by even lengthier accounts, over the preceding two years, of how he was "fighting" oesophageal cancer. They occupied four pages in the Times over five consecutive days and featured in innumerable interviews elsewhere. Now we have a collection of essays in Gould's memory that includes contributions from four former cabinet ministers and a national newspaper editor. All this for a opinion pollster?

But Gould, as Tony Blair is quoted as saying on the cover, was not simply a pollster: "he was my pathfinder." More than any of the other gurus claimed as a decisive inspiration  the obscure Scottish philosopher John Macmurray, the American communitarian Amitai Etzioni, the British sociologist Anthony Giddens  Gould guided Blair's leadership of Labour. His The Unfinished Revolution (1998) remains by far the most coherent account of what New Labour was about. "A political advertising man has taken the place of generations of socialist philosophers," observed Anthony Seldon in his Blair biography, published in 2004.

Gould either invented or brought into common usage most of the phrases and buzzwords that characterised the Blair era: "one nation", "renewal", "the future not the past", "the many not the few". He may not have been first to use "New Labour" as a compound noun  that distinction is rather opportunistically claimed in this book by Patricia Hewitt  but he used it in internal party memos as early as 1989. Nor was he the first to use focus groups, but he used them more systematically than anybody before him. Blair cut Labour adrift from its old moorings in the unions, which once provided a two-way connection to popular thinking. As James Purnell observes in this book, Gould's focus groups did the work instead, with their convenor arguing and confronting as well as listening. In The Unfinished Revolution, Gould wrote: "I see them as an important part of the democratic process."

Gould died weeks before Christopher Hitchens at almost the same age and from the same cancer. But where Hitchens memorably observed that, to the question, "why me?", the cosmos scarcely bothered to reply "why not?", Gould demanded to know the "purpose" of his illness. Since it proceeded roughly in parallel with the decline and (probably) final demise of New Labour, one may surmise that, if cancers have a purpose, this one's was to act as some kind of metaphor. This volume, which includes two contributions from pro-Cameron Tories who explain how Gould's insights helped them (almost) win an election, therefore reads as an elegy for New Labour as well as for Gould.

There is inevitably some sanitising of the past. Most amusingly, Peter Mandelson marvels at how Gould never made enemies and plaintively asks "why couldn't I manage this conjuring trick?" In fact, as Seldon's Blair biography recalls, Gould was regarded by traditionalists as "a kind of evil witch doctor", and even some Blairites disliked the apocalyptic manner in which he was apt to interpret his focus group findings.

More seriously, several writers claim that Gould was a consistent optimist: he had "an extraordinary gift for hope", says one of the Tories, Danny Finkelstein. Yet he held a distinctly pessimistic view of what was possible for Labour. His underestimate of the party's strength after 1994 sent Blair into office with a more cautious and defensive attitude than was necessary. So profoundly did New Labour internalise Gould's lesson that it must accept the principles of the Thatcher era that, even where it attempted modest redistribution from rich to poor, it kept quiet about it. As Finkelstein observes, Gould treated every day as though it were a referendum on Blair's leadership. The result was that, even with eight years of three-figure majorities, New Labour allowed Tory assumptions and arguments  taxes bad, markets good, public sector inefficient  to set the agenda and be treated as common sense.

Gould's rebranding of Labour was a work of genius. How sad that he never applied his abilities to presenting public services, taxation and welfare in a more positive light. It wasn't a big ask. Opinion polls from the late 1980s consistently showed large majorities against privatisation and, as YouGov's Peter Kellner once observed: "in 1997, most people expected Labour to put up taxes anyway, even though it had promised not to do so." But Gould never gave Labour the tools to change the political culture. In 2007, George Osborne secured a poll bounce for the Tories by promising a dramatic rise in the threshold for inheritance tax, a "burden" that fell on less than 10% of the population and, in most cases, lightly. Gordon Brown was panicked into calling off a general election and Alistair Darling into a counter-move that eased the tax in a different way. Like the US Republicans, the Tories branded inheritance tax as "death tax"; neither Gould nor any other of New Labour's much vaunted team of spinners offered an effective defence.

In the only essay in this volume that approaches a critical account of Gould's achievements, Purnell writes: "The danger of arguing within your opponents' assumptions is that you win the skirmishes but lose the war. We were doing good Labour things. But we weren't winning a common-sense argument for Labour." The party had nothing to fall back on when the economic storm broke and the Labour things stopped being good. "Without Labour roots, the saplings of the third way didn't stand a chance."

Gould rightly told Labour that it should speak to "ordinary people", mostly middle-class or expecting to become so, in their own language, divesting itself of the class-war rhetoric of the 1970s and 1980s. He was wrong, however, to insist that must mean the language of populist neoliberalism. Judging by this volume, most of New Labour's brightest stars have failed to learn that lesson.