UNTIL June or July of last year, Jeremy Corbyn had never expected to lead the Labour party and probably never wanted to. A veteran backbencher and diligent constituency MP, the 66-year-old socialist would probably have been content to go on championing the various causes – from trade union rights to Palestinian solidarity – that had defined his modest career up to that point. In his spare time, he might have tended to the vegetable patch in his north London allotment or cultivated the olive tree in his back garden.

But history had other ideas. As Richard Seymour shows in this laser-sharp analysis of British "Labourism" and its contradictions, Corbyn found himself, almost by accident, in the right place at the right time. (Or in the wrong place at the wrong time, depending on your perspective.)

According to Seymour, a prominent left-wing blogger and journalist, Corbyn’s success in last summer’s Labour leadership election represented a structural backlash against Blairism. Not only did Tony Blair and Gordon Brown hollow Labour out from the bottom up (party membership fell from 400,000 in 1997 to 170,000 in 2007), they shed millions of working-class votes and eroded the party’s historic links to the trade union movement.

This process of internal decay was compounded by New Labour’s strategy in office. Blairism advocated tight spending constraints (during his first term as Chancellor, Brown sliced £34 billion off Britain’s national debt), foreign military interventions, authoritarian policing, and deregulated financial markets.

Seymour demolishes some of the key so-called achievements of the Blair era. Blair may have introduced the minimum wage, but he did so at the “pitiably low level” of £3.60 per hour. He may have cast himself as progressive on the issues of multiculturalism and equality, but between 1996 and 2004 “racial incidents more than quadrupled in England and Wales.” He may have claimed to be a social democrat, but he implemented welfare reforms that punished single mothers, the disabled and future retirees. “Tony Blair,” Seymour argues, “did far more than Margaret Thatcher to diminish support for redistribution and turn large numbers of people against the welfare state, precisely because he led a party that communicated with people whom Thatcher never could.”

It was into this void that Corbyn – the left’s token leadership nominee – stepped nine months ago. Propelled by a generation of new, predominantly young Labour activists, he won the race to succeed Ed Miliband by a massive 40 point margin in the first round of voting. Conversely, the Blairite candidate Liz Kendall, a favourite of the London media class, finished last with less than five per cent of the vote. Seymour sees Corbyn’s victory as unparalleled in modern Labour history: “It does the novelty of the situation no justice at all to compare Corbyn to Michael Foot. Foot was of the soft-Left, and his political roots belonged in a form of radicalised liberalism … Jeremy Corbyn is one of the last standing Bennites.”

Since being elected leader, Corbyn has faced one crisis after another, including a frontbench split over British military involvement in Syria and a bitter, ongoing controversy concerning allegations of anti-Semitism on the radical left. Most Labour MPs remain hostile to his leadership, but any effort to dislodge him – in the short term, at least – is unlikely to succeed: his support among party members is going up, not down, and polls suggest he would beat any prospective challenger with ease.

However, Seymour is not optimistic about Labour’s electoral prospects under Corbyn, nor does he anticipate a decisive breakthrough for socialist politics in the near future. Even if Corbyn were able to navigate his way into Downing Street, his government would run the risk of "syrizafication", “a process wherein the radical Left is swiftly chewed up and metabolised by the institutions it seeks to govern, becoming in effect an instrument of the neoliberal centre that it was elected to replace.”

If Seymour is correct, then perhaps the best Corbyn can hope to achieve is a gradual realignment of the English political landscape to the left (Seymour views Scotland, which is covered only tangentially throughout the book, as a virtual write-off for Labour.) Given the strong conservative currents

Corbyn is fighting against – both internally, within his own party, and externally, at the electoral level – that would represent a sizeable accomplishment in itself. “Corbynism,” Seymour concludes, “will struggle to outrun the limits of Labourism.” This book is a terrifically astute – if frequently demoralising – assessment of just how suffocating those limits can be.

Corbyn: The strange rebirth of radical politics by Richard Seymour is published by Verso, priced £12.99