It was a croquette of pig's head that finally forced me to recognise the threat posed by the blogosphere. It was served at the Westerly, a restaurant in Reigate, Surrey, in April last year. I knew nothing of the place, or its chef, but I had a copy of the menu, and it was full of things I like to eat: Jerusalem artichokes and wild garlic, snails and pigeon and Amalfi lemons. It had the potential to be everything a newspaper restaurant critic dreams of - a genuine find outside London, serving terrific food at a reasonable price.

It was all that and more. I wasn't the only one who thought so. My companion agreed. Simon Majumdar, a one-time publishing executive, is a food blogger. We had met on internet food discussion boards, which he had left behind in favour of his blog, Dos Hermanos, so named because he writes it with his brother, Robin. It is their account of eating out across the world. A restaurant critic needs a companion, and Simon had regularly been mine. We both adored the gazpacho and the rillette, the lamb with its butter-rich mashed potato and the sorbet made with Amalfi lemons. And of course we loved the pig's head croquette with sauce gribiche, for we are both men with a taste for the cheaper cuts. At the end I asked for a copy of the menu, paid the bill and we went home.

Within two hours of getting back to my desk, Simon's review was online. He did not explain why he had been there. He did describe it as his best meal of the year so far. My eye strayed to his mention of the pig's head, with mounting panic: 'a large disc of head meat fried perfectly in crumbs to a crisp coating which when punctured gave off a steamy aroma of pork'. Spot on. Simon might not have been paid for it, but he is a good writer. And a lot of people would read him. Granted, not as many as read The Observer. Even today, with the cult of the Dos Hermanos blog fully developed, it rarely gets more than 7,000 readers a week.

The problem was that his readers would be opinion formers: not just chefs, restaurateurs and food journalists but other hardcore restaurant goers. And when my review was printed almost three weeks later they would all assume I was the one who had taken my lead from Simon rather than the other way round; that the real finds were being made by the amateurs. The blogger had beaten me into print. I had no choice. I called Simon and asked him to take down his post until my version had appeared. Ever the gentleman, he agreed. From that point on I concluded I could no longer view the blogosphere as source material or even mere displacement activity. Now it was the competition.

It could be worse. At least those of us in Britain who make our living from our opinions are still gainfully employed. Across America it's a different story. Paid newspaper critics from a number of disciplines are being laid off or redeployed, their judgment deemed superfluous to requirements in the age of the net. Book review pages are becoming increasingly skinny. Television sections are disappearing. In April, Sean Means, the film critic of the Salt Lake Tribune in Utah, used his blog to publish a roll call of his movie-reviewing colleagues who, since the spring of 2006, were no longer in the opinion business: 'Steve Ramos, Cincinnati CityBeat, position eliminated ... Jami Bernard, New York Daily News, contract not renewed ... Michael Atkinson, Village Voice, laid off ...' At that point it ran to 28 names across the US media but since then it has stretched inexorably on.

Others soon started taking notice, with both the entertainment industry journal Variety and the Los Angeles Times publishing large pieces on the death of the critic. As Patrick Goldstein put it in the LA Times: 'Critics are being downsized all over the place, whether it's in classical music, dance, theatre or other areas of the arts. While economics are clearly at work here - seeing their business model crumble, many newspapers simply have decided they can't afford a full range of critics any more - it seems clear we're in an age with a very different approach to the role of criticism.'

It appears that consumers no longer feel the need to obtain their opinions from on high: the authority of the critic, derived from their paid position on a newspaper, is diminished. Opinion has been democratised. In the movie world two sites are credited with decimating the profession. Ironically, Rotten Tomatoes, founded in August 1998, was designed to give readers access to the opinions of a bunch of critics. If 60 per cent or more of the reviews are good, the film gets a fresh rating; fewer than 60 per cent and it's rotten. The site became so popular that in 2004 it was bought by IGN Entertainment which, in turn, was bought by Rupert Murdoch's News Corp (which, as a newspaper publisher, also pays critics). Metacritic, launched in January 2001, also combines reviews but across various media and arts, including films, video games and books. It too became so successful it was bought out, by CNET networks. Since then, blogs, written by unpaid enthusiasts, have proliferated to such a degree that in some areas of the arts their writers are being courted by the PR machine.

The old media have, predictably, been outraged. After all, their jobs are on the line. 'People who make these decisions,' says Sean Means of the host of sackings, 'get it into their heads that people who want to read about new movies have lots of places to do so, from fan sites, through blogs to critical aggregators, but they are being short-sighted. The reason people buy newspapers is to hear that particular voice.' So is he saying that the opinions expressed for free on blogs are not of value? Not necessarily, he says. 'The truth is, though, that there are very few amateurs who are better than professionals. If you really are good at it you figure out some way to get paid for it. At the risk of sounding elitist, everyone has an opinion, but not everyone has an informed opinion.'

The advent of the net has been described as a revolution. If so, one of its most heated battles is being fought over the right to claim expertise. In the US the ancien régime, in this case the salaried critic, appears to be in retreat. The question is what will happen here? We need only look at television criticism, a once-noble calling pursued for this newspaper by both Julian Barnes and Clive James, for clues. In May the Daily Telegraph decided it no longer needed a daily TV review. Regular TV reviews have also gone at the Daily Mail, Mail on Sunday and London's Evening Standard. Could the same happen to other arts?

The British critical tradition is long and rich and deep: from the pamphleteering of Joseph Addison and Richard Steele in the early 18th century, through the literary criticism of Oscar Wilde in the 19th to Graham Greene's film reviews and Kenneth Tynan's first-night theatre notices in the 20th, we have never been short of confident people to tell us what is good and what is not and why.

'We have a wonderful tradition of criticism in this country,' says Brian Sewell, art critic of the Evening Standard for nearly 25 years, 'and it would be a tragedy if we lost it. The onlooker sees most. We are the skilled onlookers.'

But in a globalised world where something posted on the net in Chicago one minute is read in London the next, no trend is ever localised. So how web-savvy are Britain's crew of professional opinion-peddlers? Are they ready to take on the challenge from the ones who do it for free? There's only one way to find out: ask them. So we assembled a collection of Britain's longest-serving and most distinguished paid critics who, between them, have more than two centuries' experience in telling us what they think, and sought their opinions. It's what they're for.

Andrew and Phil have lots of opinions too, and tonight I'm hoping to hear some of them. It is a warm evening in Waterloo and we are at the Young Vic for a preview performance of Berthold Brecht's The Good Soul of Szechuan, starring Jane Horrocks, a gritty little number full of cement dust, exploitation of the workers, prostitution and discordant, irritatingly Brechtian songs.

Of course, paid newspaper critics do not review productions on previews, but Andrew and Phil - they insist on first names only, to maintain the web-enhanced 'mystique' - are not paid by anybody. They write a blog called the West End Whingers, which they set up in June 2006 after sitting through what they regarded as an appalling production of Sam Shepard's Fool For Love, starring Juliette Lewis. Both middle-aged, long-time theatregoers, they were fed up with each other's whingeing so, as they explain on the blog, they 'decided to whinge at the world instead'.

Their reviews, written under one voice, are sharp and irreverent in a mannered, high camp sort of way. Their destruction of Michael Frayn's Afterlife at the National Theatre, written for the most part as a play about the imagined receipt of the script, is laugh-out-loud funny - and a damn sight more enjoyable than the hand-wringing from some of the paid critics when they held forth over what was agreed to be a sub-standard work by the revered playwright. ('[Frayn's] deliberately repeated bits over and over again,' they imagine National director Nicholas Hytner howling, 'I knew I shouldn't have given him a word count. It's the oldest trick in the book.')

As we wait for The Good Soul to start I ask them if they feel they have a responsibility to anybody. (As with the no-surnames rule they also insist on being interviewed as one person, while telling you that they have never been a couple.) 'We're only here for our own amusement,' they say. 'We have no obligation to sit through it on behalf of our readers.' Walking out of plays is a speciality of the West End Whingers. If they don't like it, they leave. After all, their tickets aren't free. They have paid for almost every one, bar those for Swimming With Sharks starring Christian Slater. 'We didn't care for it and we said as much. We haven't been invited back to the West End since.'

Their beautifully described midway departure from an early preview of the epoch-long Gone With The Wind was, according to a number of people in the theatre world, the first sign that all was not well with the musical. So do they think the mainstream critics have a role? 'Oh yes. Someone has to stay until the curtain to see what happens at the end.' Would they like to be paid for what they do? 'I think if we were paid it would mean we would have to play the game, which would be boring.'

They also have no desire to work for a newspaper. 'Endure the theatre without alcohol? Locate things in the wider discourse? No. we have no aspirations in that direction.'

There is quite a lot of alcohol tonight: before, during and after as the whingers and their entourage - me, other bloggers, a few friends of friends - settle in to enjoy themselves. Their review, when it is posted a couple of days later, seems to reflect a good night out. 'Horrocks was great and there were many other performances to enjoy, too,' they wrote. 'In fact there were oodles of things to write down: great wigs, a lot of cigarette smoking, rain, wonderful props and signage...' So no, not exactly a first-night crit of the sort Kenneth Tynan might admire. But - whisper it - it did quietly remind me more of the night I'd had than did the professional reviews I would later read.

Which is all well and good, says Charles Spencer, a theatre reviewer for the Daily Telegraph since 1991. But that doesn't mean we should mistake what the West End Whingers do for criticism. (Which, for the record, they never claim it to be). 'I don't think they're very helpful,' Spencer says. 'Mildly entertaining, I suppose, but that brand of camp humour doesn't do it for me. They're not really critics. The last thing of theirs I read was them whingeing about squeaky seats at the Old Vic.' Then again, Spencer admits to being a bit of a web-refusenik. 'I look at Wikipedia now and then but until a year ago I hadn't looked at the web at all.'

Indeed it would be easy to portray many of our leading critics as a bunch of silver-backed elders of the tribe, caught on the hop by technological change. Of course, just because it's easy doesn't mean it's the wrong thing to do. Gillian Reynolds, who has been writing superbly about radio since 1967, and for the Telegraph since 1975, admits she has little time for opinions on the web. 'I just don't want to hang around with company I don't value. Life's too short.' Clement Crisp, who has been writing about dance for the Financial Times for more than 35 years, and for whom the word 'venerable' might have been invented, is succinct about it: 'I don't really understand the beastly internet.'

This is not to suggest that Crisp dismisses what bloggers are doing. 'The people who are writing these reviews are absolutely splendid,' he says, letting the last word sing for slightly longer than the other nine put together. 'They are devoted ballet fans. But it has nothing to do with criticism.' The point, he says, is that the true critic can draw on a well of experience. 'I started going to the ballet as a child in 1943, and for the next 20 years I saw everything there was - the creation of the great new companies, the arrival of the Russian, the Danes ...' Only then did he begin to write.

Spencer agrees. 'You're supplying a service, one with real authority behind it. There is always going to be a need for expert opinion.'

Don't even mention the need for the democratisation of opinion to Brian Sewell. 'I do not believe in the democratisation of opinion. I believe in benign authority. And if we undermine the authority of critics then we shall descend into mayhem.'

Our own Philip French, film critic for The Observer for 30 years, is a little more accepting of the challenge from the bloggers. 'People should have the right to express their opinions. The right to free speech has been extended, but you don't have to be elitist to say that not all opinion is of equal value. There is good criticism and there is bad criticism. The risk is that bad criticism will drive good criticism out of business by sheer volume.'

Michael Billington, the Guardian's theatre man for more than 35 years, allows that there is a new accommodation to be made. Then again, he works for the publishers of this newspaper which, historically, has embraced the online world with more enthusiasm than others. He has been forced to join the debate on the web. His first piece for Guardian Unlimited (now theguardian.com) was about The Sultan's Elephant, a public art installation involving a huge mechanical pachyderm striding through London in 2006. 'I wrote a piece attacking it and got hundreds of comments. They clobbered me. I wasn't used to getting such a response.' It was a wake-up call. 'I was suddenly aware that there was an army of people with opinions as strong as mine. Journalists of my generation have to adapt. And we have to accept that the printed word no longer has aristocratic supremacy.'

Of course, some newspaper critics are living the digital life to the full. Both Mark Shenton, drama critic of the Sunday Express, and Ian Shuttleworth, of the Financial Times, either blog or weigh in on other blogs. Norman Lebrecht, arts columnist of the Evening Standard, has long written a blog for artsjournal.com and is an avid consumer of online opinion. 'What I see out there is quite a mixture. A lot of it is amateurish in a good sense. But I do miss incisiveness, people delivering real information and knowledge.' He also counsels his brethren to think twice before wading in to online discussions. 'One has to be very careful of making any comment. Bloggers are as sensitive as any diva. Criticise them and they will attack you.'

Sometimes they will attack without any encouragement. Gareth James is a freelance management consultant who has been writing reviews at whatsonstage.com for six years. There is, he argues, a shift in power towards the consumer. 'I simply started disagreeing with the critics,' he says. 'They are out of step with the audience and that's because they do it all the time. Most people go to be entertained. We go to have a good night out.' Critics, he thinks, go for something else. It's why he believes they write enthusiastically about the works of Pinter or Chekhov which, for the most part, he can't abide. 'That sort of thing is put on for the Michael Billingtons of this world, not for Gareth James.'

It was a similar sense of disconnection that got Lynne Hatwell writing her book blog, Dove Grey Reader. A community nurse with a major reading habit, who lives in the Tamar Valley on the border of Devon and Cornwall, she increasingly felt the books pages of national newspapers had nothing to offer her. 'I had this feeling there was a literary feast going on in London but that I was not a part of it. I also didn't feel I was being well served by the bookshops, that I had become a puppet of their three-for-two tables. I wanted to know how you find other stuff.' Now, according to her 'what I'm reading' panel, she is working her way through Trauma by Patrick McGrath, Trying to Please by John Julius Norwich and, er, my latest one. Hell, the woman's far too influential for me to let that opportunity pass me by.

She declares that she is not a literary critic or reviewer. She writes about what books mean to her. 'There's nothing objective about what I'm doing. I used to worry about whether what I felt about a book was the same as anybody else.' Not any more. 'I feel a responsibility to myself, to be transparent and honest, but also to the readers because there are some who now compile their reading lists solely from my recommendations.' Is she posing a challenge to the books pages of national newspapers? 'Absolutely, and one that was long overdue. For too long it was a closed shop.'

But, she says, the project was personal. In the first year she spent more than £2,000 on books. But publishers set up Google alerts, which mop up any mentions of their titles online. Soon she was receiving emails offering to supply her with details of new publications. She now gets nearly all the catalogues and free review copies of books from most publishers (except, curiously, Virago, which ignores her - but probably won't after reading this). 'I've realised that I could be used as a marketing tool, and I have to resist that. A fundamental rule is that reading still has to be a pleasure.' Also, she doesn't do bad reviews. If it's on her site it's because she likes it. 'It's about my emotional responses.'

Other sources of critical opinion have risen up online, their creators say, because the old media wasn't able to handle them. Steve Bennett created chortle.co.uk, an online stand-up comedy fanzine, because there was not enough coverage in the press. 'Even the mags that dedicated space to comedy didn't give it much space.' Everybody did Ricky Gervais on tour. Everybody did Bill Bailey and Lee Evans. Nobody did the smaller names. 'To do a print version of Chortle would be very expensive whereas an internet start-up is cheap.'

Naturally, comedy publicists take notice of chortle, but it's in film where the real PR action is. Jam, a digital marketing agency, targets bloggers. For Daniel Noy, an executive with the company, utilising their power is a no-brainer. 'Bloggers are important because of the way the internet started. It's a community, which means there's a community of film fans online.' The challenge, he argues, is to know how to use them. 'There's a wariness about bloggers, a sense that you can't control them. Personally I don't think that you should control them. Reactions can be good or bad. It's a risk you have to take, and that's the power of real conversation.'

Jam has begun blogger-only screenings, starting with Juno. 'It helped that Diablo Cody, Juno's screenwriter, was a blogger.' But the digital marketers have to be honest. Back in 1999, the Jurassic age in web terms, Warner Brothers wanted to hold a test screening for the Will Smith movie Wild Wild West to build buzz on the net, but was so unsure of the film that it told the invited audience of online critics that they were going to watch The Matrix. The audience was furious and helped create the negativity around it that never dissipated. 'They posted comments slagging it off and it did very badly.'

So does Noy think newspaper critics are now redundant? Not yet. 'You can't deny the readership of newspaper and magazines.' Chortle's Bennett agrees. 'A lot of newspaper critics have got the job because they both know what they are talking about and can write,' he says. 'Where as a lot of bloggers may only fill one side of that equation.'

I wondered if my sometime dining companion Simon Majumdar agreed. When his last employer went bust he decided to explore the world's eating opportunities. He came up with an idea for a book, Eat My Globe, which is out next year. He is now a paid food writer. Does he think the democratisation of opinion is a good thing? 'You can get as many opinions as there are arseholes. Everyone's got one. There are some good writers out on the web. Then there are some who shouldn't be allowed to write an address on the front of an envelope.'

So the professionals still have a role? 'I like reading you all but I don't think any of you necessarily know more about food than I do. I read you for entertainment. If you're not entertaining, however informative you are, there's no reason for you existing.' In short, he says, we can claim authority only by being good.

Finally, I alight on the killer question. Simon, would you like my job? 'If I had the opportunity to take your job away from you,' he says, 'yes, I would.' That is a reassuring vote of confidence in old media. More reassuringly, there isn't a vacancy. At least for now.

Additional research by Maria Garbutt-Lucero and Katie Toms