'Cameron has been one of the most disappointing Conservative leaders." During his tenure, "error has been piled upon error". His party is still seen as "a party of the rich". His big society "has been a complete failure as a message". In office, as well as lacking a plan, his party "has lost a sense of social justice … Conservative rhetoric often borders on social Darwinism". Instead of "a rightwing party with a heart", Cameron has "created a centrist party with cuts".

Even after months of Tory troubles, it is still something of a shock to hear these things from a lifelong Conservative. And not from some disgruntled activist or marginalised, anonymous cabinet dissident, but from one of the party's dominant figures, on the record, in the New Statesman, this newspaper and the Spectator over the past 12 months.

Yet Tim Montgomerie is not like previous important Tories. Instead of a parliamentary constituency or ministry, or a personal fortune used for strategic donations, he has an unofficial party website, ConservativeHome, and an increasing ubiquity in the rest of the political media. At 42, he is a fluent, seemingly inexhaustible writer, broadcaster, thinker, alliance-builder and campaigner. Over the past dozen years, he has played multiple, apparently contradictory Tory roles: internal critic and cheerleader; intimate of the party elite; self-appointed voice of the grassroots; polemicist for a more populist Conservatism – sometimes more, sometimes less right wing – and dispassionate analyst of the party's ups and downs.

"It's a new role in British politics," said Max Wind-Cowie of the Progressive Conservatism Project at the thinktank Demos. "Without being elected, originally without the endorsement of a national paper, standing outside the official structure of one of the main parties, he has established himself as one of the foremost voices about what that party should do."

Robert Halfon, Tory MP for Harlow, who has known Montgomerie since university, said: "I've never met anyone like him. He's got so much energy in his head. He is a political entrepreneur."

Montgomerie founded the ambitiously named ConservativeHome in 2005. Since 2009, it has been funded by the wealthy, perpetually manoeuvring Tory peer Lord Ashcroft. Edited by Montgomerie and four other staff, written by them and scores of contributors, it serves as a unique one stop shop for hundreds of thousands of rightwing Britons. "ConHome", as it is known in Tory circles, offers punditry, gossip, political philosophy, policy wonkery, a comprehensive roundup of Westminster news, appeals for help with Conservative causes, sales pitches from ambitious MPs, and sometimes raw contributions from party members and supporters.

"I and almost everyone else I know in the party read it at least once a day," said Wind-Cowie. Jesse Norman, Conservative MP for Hereford and South Herefordshire, said: "Very few younger MPs don't check it." Halfon added: "There are a lot of people in the Commons who say 'we don't look at it' when they look at it 50 times a day." Wind-Cowie, Norman and Halfon are all contributors – few prominent youngish Tories are not – but the site is also respected by bloggers on the left. Sunny Hundal, editor of Liberal Conspiracy, said: "As a political operation I think ConHome sets the benchmark for everyone else."

One well-connected Tory-watcher calls the site "a party within a party". A Tory MP said: "Being a ConHome reader has almost replaced the party membership. I don't think I've looked at the official Conservative party website for about six months."

Strikingly, senior Tories heavily criticised on ConservativeHome, such as the former health secretary Andrew Lansley, the former Tory chair Lady Warsi, and the former justice secretary Ken Clarke, often lose their jobs. On BBC Question Time in February, Clarke railed against "Tim Montgomerie, who sets himself up as representing every active Tory in the country on his blasted website". Sometimes mockingly, sometimes fearfully, many Tories have started referring to Montgomerie as "the high priest of Conservatism".

In truth, ConservativeHome is a little too broad in tone and content to be simply a personal mouthpiece. It publishes hostile reader responses to Montgomerie's more controversial stances, such as support for a wealth tax ("This is madness") and gay marriage ("You've sold your soul"). Yet an argument for a particular sort of Conservatism pervades the site. Montgomerie and his online allies are sceptical about the EU, and about Cameron and his Tory "modernisation", which they consider too metropolitan and – gay marriage aside – too socially liberal. Most Britons, they argue, want the Conservative party to be tough on crime, welfare and immigration; but also more socially concerned and less elitist – "rightwing with a heart", in Montgomerie's phrase.

"He's got a robust, highly intelligent, well-organised critique of Conservatism from within the right," said Norman. "The hybrid that Tim is pulling together is … rediscovering arguments from the 80s and 90s, but explicitly actuated by concern for the less well-off. The political effect of that is to reach out across political, class and emotional lines."

Recently, there have been signs that the government is paying these ideas close attention. "Conservative methods are not just good for the strong and the successful but the best way to help the poor," Cameron told his party conference this month. Montgomerie and ConservativeHome were even more prominent at the event than usual, their large, showily positioned marquee hosting events featuring Tory stars such as Michael Gove, Iain Duncan Smith and, most noisily, Boris Johnson – whose party leadership credentials Montgomerie has been pointedly talking up in recent months.

At Tory gatherings, Montgomerie is easy to spot: tall, more casually dressed than more conventional Tory players, speaking in a seductively calm voice that combines politeness and attention-getting jolts of candour. At conference this month, "he was just king of the whole place, striding about as if he really was running the party", said one attendee.

Montgomerie denies any such intention."I do not want ConservativeHome to be a party within a party," he said. "I want it to be the conference fringe that never stops." Have he and the website prompted the Tories' current populist turn? "It is possible that I was a little bit ahead of time … on the need for the party to support Britain's strivers. But the focus groups and opinion polls have been telling them similar things."

Conservative unpopularity, and trying to find ways to end it, have been the near-constants of his political life. Born into an army family in Hampshire in 1970, his politics were Tory from the start. But his teenage Thatcherism was tempered, he says, by discovering evangelical Christianity at 16. At Exeter University, he helped run the Conservative Association with Halfon and two other current Tory MPs, Sajid Javid and David Burrowes. It was the end of the 80s and support for the Tories was ebbing. "We used to talk about making the party not just for the rich," said Halfon. "Tim had a BBC computer with an old-fashioned printer. He'd produce leaflets, newsletters, posters. A complete workaholic. ConHome is just an outgrowth of that."

At Exeter, Montgomerie and Burrowes also started the Conservative Christian Fellowship, a still-extant organisation for uniting and expanding the party's Christian membership. Influenced by the US religious right, Montgomerie fiercely promoted what he now calls "traditional views on homosexuality. That was my upbringing. I don't hold those views any more." After working briefly in the 1990s as a Bank of England statistician – for a polemicist, he retains an unusual, and potent, zest for figures – Montgomerie moved into full-time politics at Conservative central office, first under the leadership of William Hague, then under Iain Duncan Smith. Influenced by the "compassionate conservatism" of pre-9/11 George W Bush, Montgomerie saw his mission as strengthening the Tories' social conscience while keeping them as a strongly rightwing party. Duncan Smith increasingly relied on him, first as a speechwriter, then chief of staff. The fact that Duncan Smith's leadership went so badly has provided ammunition for Montgomerie's enemies ever since. As one MP put it: "Tim is part of the problem, not part of the solution, some would say. The last time he had influence, the party was not in a beautiful place."

To some of his critics, Montgomerie combines a restless search for ideological purity with electoral naivety: "The Conservative version of Michael Foot's Labour party," wrote Matthew Parris in the Spectator last year. Others find Montgomerie's ever-quotable outspokenness sly or baffling or self-indulgent, given the already-buffeted government. "He does cause a lot of angst, particularly in No 10," said the Tory blogger Iain Dale. "But they still deal with him." Montgomerie is still invited to Downing Street drinks parties, and Cameron still talks to him at them. "They are civil, but you can tell there's an underlying grievance," said one observer.

Few doubt that Montgomerie would prefer a different leader. He was one of the earliest and strongest Tory pessimists about the party's chances at the next general election, and ConservativeHome, some Tories speculate, will play a pivotal kingmaking role if Cameron fails to win. Montgomerie said carefully: "One day, we could bring two huge assets together, Boris, as a presidential PM, and the [very rightwing] class of 2010."

Yet Montgomerie is a more complex person than sometimes imagined. Disarmingly mild-mannered, he "never forgets if he feels you've let him down", said Halfon. A veteran Westminster player, he lives in Salisbury, not London, most of the week, in the same otherworldly cathedral quarter as the former residence of Edward Heath. He is single, and able to work six days a week, he says, following "biblical principle": on the seventh, he gets the train with his sister to watch Manchester United and their famously Labour-supporting manager.

Like many obsessive activists – Montgomerie insists he never wants to be an MP – he oscillates between optimism and pessimism, dissidence and loyalty. He recently launched another website, strongandcompassionate.com, straightforwardly dedicated, it appears, to campaigning for a Tory majority in 2015. He has described his political trajectory as a journey. He said: "Perhaps I've moved leftwards on the NHS and rightwards on crime."

His long-term ambition, he said, "is for ConservativeHome to be handed over to someone else" to run. Then what? There is an uncharacteristic pause. "Maybe something in the [international] development world." Whoever is Tory leader then may breathe a sigh of relief.

Highs and lows





Born 24 July 1970

Career Son of a soldier who discovered Thatcherism and Christianity in his teens, rose and then fell as an influential behind-the-scenes Tory, then reinvented himself as a new kind of political player through ConservativeHome.

High point Predicting before the 2010 general election that the first-ever televised party leaders' debates would be "a big boost for Nick Clegg", and that the Tories might "live to regret" agreeing to participate.

Low point Failure, as Iain Duncan Smith's chief of staff, to help protect the Tory leader in 2003 from an internal party coup has been cited ever since by critics who say he is too cerebral and naive.

What he says "I'm not worried about ConservativeHome being too powerful. I'm worried that I'll wake up tomorrow morning and find a group of Conservatives with a lot of money behind them have launched a rival."

What they say "He's a natural politician," says one well-briefed Tory journalist. "He'll make an alliance with anyone on a single issue. What if he had become an MP in 2001 like Cameron and Osborne? It was an incredibly weak intake; had Montgomerie been there, Cameron and Osborne would have had more competition since."