As the nation's most recognisable movie reviewer, Mark Kermode is a pretty busy guy. Recently named as The Observer’s chief film critic, he balances writing with his duties as one half of Radio 5 Live’s flagship review show, simultaneously contributing content to Sight & Sound, The Culture Show, Newsnight Review and the BBC. Not to mention, of course, the fact that he spends an unhealthy (read: enviable) amount of time in darkened screening rooms. Somehow, though, the good doctor also finds time to function as a published author, with his latest book, the snappily-titled Hatchet Job, focussing on the current state of film criticism.

Say what you want about Kermode – and plenty have – but his enthusiasm for film and film criticism is infectious. It’s nearly half-past ten when our interview takes place, and the outspoken broadcaster would have been forgiven for calling it a night. After all, he's already spoken on stage and performed a lengthy question-and-answer session, before taking the time to speak with each and every fan that waited in line to have their book signed. A line, it’s worth noting, that snaked so far across the auditorium it was like opening night for a new Lord of the Rings movie. But while a cold Peroni and an old friend await him at the bar, Mark kindly agrees to one more discussion.

'I think informed opinion is important', says Kermode, explaining why he believes professional critics are still necessary in a day and age where everyone is a blogger. ‘Just because we’ve gone from print to digital, doesn’t mean you have to dispense with values. Clearly some people thought, "Why should we pay film critics? We can just get somebody off the web to do it." Well the reason is, as the guy who was in charge of The Chicago Sun-Times said, "quality journalism is not for free", and it isn’t.’

Being a professional critic is something Kermode is fiercely proud of. It is, as he explains, a position that also requires putting in the hours. ‘It’s very hard to get into the A-list. When I first started working there were A, B, C and even D lists you’d have to work your way through. It was a catch-22. You had to be published to get into screenings, but you couldn’t get into screenings unless you were published.’

Such problems are now long behind Kermode, who was voted as the nation’s most trusted film critic a few years ago. Modest and self-deprecating, he reminds everyone that he only received 3% of the vote, going on to credit 5 Live partner Simon Mayo – the Watson to his Holmes – as the reason he's had so much success in radio. Now on his third book, Kermode uses Hatchet Job as a platform to wave the flag for professional criticism, assessing the relevance of critics today while examining the impact of memorably harsh reviews.

'In the case of Hatchet Job, I just started writing about negative reviews, and why it was that negative reviews stuck,’ he says. ‘I write all the time because I write for The Observer and Sight & Sound, but you’ll find yourself writing something and it doesn’t fit anywhere. So you just fit it away in a file, and then a little widget of it will turn into something.’

As with the book, Kermode makes more digressions than Alan Partridge. But each tangent is fascinating and insightful in its own right, powered by an obvious passion for cinema and an encyclopaedic knowledge of film. That said, Kermode is keen to point out he doesn’t have all the answers, having been quizzed about a potential solution for the ever-shrinking amount of coverage and funding afforded to arts journalism. ‘The honest truth is I don’t know. That’s an economic question. I don’t know because in the end I’m a critic. And I do think there’s a problem with critics attempting to solve the problem.’

Another ‘problem’ within the industry, he argues, is the inconsistent level of access afforded to critics. ‘At the Cannes film festival, the whole white, blue, pink or pink-with-a-yellow-dot card system is completely nuts. I know really, really hard-working film journalists who file for very reputable publications and end up in the most terrible scrum situations. Whilst people who have, as far as I’m concerned, far less reason to be in those screenings, waltz through with pink passes with yellow dots on.’

‘That’s one of the reasons why I can’t stand the Cannes film festival,’ he continues. ‘I did six years at the Cannes film festival on a blue pass, working for Radio One, who I guarantee you had a bigger listenership than some of the people who were waltzing in with pink passes from television. But as far as Cannes was concerned, radio is without pictures, and therefore it’s second rate. We’d have all these conversations, we’d say, "But it’s Radio One. Do you know how many people listen to Radio One?" "Nope, don’t care. It’s radio."’

If all this sounds a bit on the grumpy side, it’s worth pointing out that Kermode is equally optimistic where appropriate. ‘Everyone improves,’ he enthuses, noting the value of critics who take the job seriously and work hard at their craft. ‘You look at Nigel Floyd, who I hold up as the great guru. When I was subbing Nigel’s copy in the eighties, it was still better than anything I’ve ever written. But as he’s gone on he’s become a better writer. He’s become more acute, more precise. It’s like anything else: if you play a violin for thirty years, you’ll get better. Reading his copy is like watching somebody playing a violin, you just go, "yup, that’s just better."’

Hatchet Job is out now, published by Picador.