Trouble in the world's influencer capital: They're rude, never say ciao and there's a three-hour wait for the best selfie. Have the preening hordes ruined Capri for good? JANE FRYER

The Grotta Azzurra, or Blue Grotto, is a vast sea cave - 200ft long, 80ft wide - set deep into the limestone cliffs at Capri's eastern tip.

Over the years it has been Roman Emperor Tiberius's personal swimming hole, a marine temple, a home for witches and monsters and, more recently, a very private swimming spot, I'm told, for Mariah Carey.

But its big moment came in 1826, when the cave was 'rediscovered' by German writer August Kopisch and his friend Ersnt Fries, after a local fisherman took them there.

Herr Kopisch was so excited by the cave's peacefulness and astonishingly blue water – caused by the sunlight reflecting up through an underground cavity – that he wrote a book, telling everyone to come and see it.

It turned out August was one of the great 'influencers' of his day – travellers flocked from all over to see the cave. But I suspect even he might be a teeny bit surprised to witness the scene now.

The Grotta Azzurra, or Blue Grotto, is a vast sea cave - 200ft long, 80ft wide - set deep into the limestone cliffs at Capri's eastern tip

It's a three-and-a-half-hour wait, in blistering sunshine, for a five-minute trip into the cave in a tiny wooden boat

21st-century social media influencers have declared the Grotta Azzurra one of the most 'Insta-worthy' spots in the world

Because it is all rather hectic.

The entrance is completely obscured behind a barrage of at least 22 power boats - some with dozens of passengers, others privately owned - bobbing in the water.

But it is the people that really grab the eye. Well over 100 of them - and most primping, preening, pouting, flicking hair and adjusting bikini tops and (in some cases) ill-advisedly cutaway swimsuits.

They suck in cheeks, arch their backs, point their toes like ballerinas but, most of all, gaze into their cameras. Taking photos of themselves. Each other. Themselves again.

It's a mass-modelling shoot. And not just women.

The men are at it, too - leaning on stainless-steel safety rails to display rock-hard abs and elaborate tattoos. Some doing the odd press-up to keep the blood flowing.

And they need to. Because it's a three-and-a-half-hour wait, in blistering sunshine, for a five-minute trip into the cave in a tiny wooden boat manned by a heavily muscled rower who will sing O Sole Mio (the Cornetto song) at the top of his voice.

But they'll happily do it, because 21st-century social media influencers have declared the Grotta Azzurra one of the most 'Insta-worthy' spots in the world. (I'm even told one Italian influencer got her big break after being arrested for illegally swimming in the cave – luckily, she filmed it before she was caught).

And this lot – mostly day-trippers who arrive on the ferry from Naples - are here to produce their own social media content and live the dream.

Other hot spots nearby are the world-famous Faraglioni rocks – three great hulks of limestone with a natural arch jutting off the coast, also surrounded by boats.

Mariah Carey takes a dip in the water in Capri

Vitorrio, 81, the crisply-dressed owner of Da Paulina, one of the island's most famous (and expensive) restaurants

'The Faraglioni are the backdrop,' I'm told by several immaculately made-up girls clutching enormous smartphones.

It's the place to be,' explains Martina, 21, a student from Sorrento, who is being styled by her friends Giulia and Elisa. 'I already have over 2,000 followers, but these are going to be the best photos.'

Of course they are. It's a gorgeous spot. But it's all been driving the locals a little bit mad.

To the extent that local mayor Francesco Cerrotta has proposed enforcing a 'ring of steel' around the island – a 330ft exclusion zone around the main coastal Instagram hotspots, to limit all the power boats and, well, calm things down a bit.

So earlier this week, I flew out to Capri – someone has to cover the hard news – hired my own speed boat and roared across the Bay of Naples with the wind in my hair to see what all the fuss was about.

I meet Cerrotta, 72, who has been Mayor of Anacapri for the last 25-odd years: the old, higher, more exclusive bit of the island where A-listers and film stars are two-a-penny and a coffee can cost €10. His white-washed office is festooned in Italian flags and pictures of the island; he has never lived anywhere else.

'We are used to visitors and used to crowds – but we need to protect our island,' he explains.

So he tells me he's thinking of putting in a big 'car park' out at sea for all the boats, perhaps with wardens.

'Maybe we'll start our own parking app!' he says.

Gosh, I can't see Kourtney Kardashian and Kendall Jenner fiddling about with that.

But the prime issue is safety. The luxury power boats, beloved of influencers, Instagrammers and A-listers alike, can cause giant waves, endangering swimmers, kayakers, paddleboarders - pretty much anyone hoping to enjoy a bit of peace and quiet.

Jane Fryer takes a boat through the Grotto Azzurra on the Island of Capri

Martina, 21, a student from Sorrento, takes a photo of her friend at the world-famous Faraglioni rocks - three great hulks of limestone with a natural arch jutting off the coast, surrounded by boats

Manuela Schiamo, councillor for tourism, who has joined us, chips in. 'We love tourists, all of them - they are our blood. But if someone drowns because of the boats, the waves, we are finished. It is over. We have to have some governance.'

There are also environmental concerns. The bigger boats smash down their anchors on to the seabed, damaging its delicate ecosystem. And it doesn't bear thinking how much fuel the boats around Capri guzzle every day.

Visitor numbers are another issue. More than 2.5million a year for an island of just four-square miles and a permanent population of 14,000.

'We are full, very full. There are queues everywhere. There is a great strain on the services,' one local businessman tells me.

This year, there have also twice been water shortages causing the island to shut down temporarily - something everyone is very quick to point out was to do with supply problems in Sorrento, on the mainland.

Even so, the proposed tightening of restrictions – with fines of up to €800 for transgressions - is causing tension.

One local has branded the mayo 'Mussolini'. Others feel it is an overreaction and that any business is good business.

Because, of course, Capri is used to visitors. Lots of them. And is totally reliant on them.

From the literati of the 19th and early 20th centuries, to the glitterati of today – royalty, pop stars, film stars - there have always been two tiers of visitors.

The elite travellers who don't flinch at €40 cocktails and €500-per-person pasta meals in flower-strewn restaurants decorated with hundreds of lemons.

And the 6,000-10,000 day trippers who come by ferry and do a whistle-stop tour of the hotspots, a bit of shopping and hotfoot it back to the mainland again.

But this latest incarnation – a new third tier of social media addicts - has had residents scratching their heads.

According to Gianni Tedesco, a big bear of a man, who owns Capri360 boat and concierge service and is my very brilliant guide for the day, the Instagram bubble started growing in 2018 and has been getting bigger ever since.

'Will it burst? I do not know. They are everywhere you look but I am an entrepreneur, I go with the opportunities. If they want help, I help. It is business.'

British actor Theo James is spotted shooting a television advertisement for Dolce & Gabbana in the Italian sunshine

Billionaire Jeff Bezos enjoys lunch oh his yacht with his partner Lauren Sanchez and friends

Others, however, are more outspoken.

Vitorrio, 81, the crisply-dressed owner of Da Paulina, one of the island's most famous (and expensive) restaurants, can't understand it.

'They only come for the blue caves and the rocks. That's all they want. It's mad. They don't see Capri!'

Antonio, who has been a fishmonger in Anacapri for the past 50 years, is more robust.

'A hundred meters [exclusion zone] is not enough. They should do two miles. Right out. Maybe as far as Napoli – 18 miles!'

Not, he insists, because he doesn't like tourists, but because the quality has gone downhill.

'Uooph! The tourists today, so rude,' he says. 'They've gone from A to Z. They don't greet you. Always looking at the screen and taking photos, but of themselves, not of Capri! In the past we had Jacqueline Onassis!' he adds, dreamily.

Ah, Jackie O, seemingly forever walking under lemon trees and hibiscus in her massive sunglasses and crisp white capri pants (which, apparently, she bought here in bulk, because she didn't like packing).

'No one will ever be like her – or her boat!' says Antonino. 'We all loved Jackie.'

Because arguably it was Jackie - aboard Aristotle Onassis's lavish superyacht the Christina O - who really cemented Capri as a magnet for glamour and money. And, ever since, it has been buzzing with A-listers who arrive by chopper, speed-boat or megayacht and spend, spend, spend.

Bradley Cooper, Ryan Seacrest, 50 Cent, Matt Damon. Dua Lipa was here last month. Leonardo DiCaprio seems to be here every other week.

'Lovely man. So low-key. He was here two days ago - you missed him. Big shame,' says Gianni. 'He books me direct using the name Jordan Belfort - his character in The Wolf of Wall Street.'

Everywhere you go, the locals adore the celebrities and are full of stories.

About how Paris Hilton is surprisingly lovely. How no one would dream of bothering George Clooney as he sipped his macchiato. How Gwyneth Paltrow loves it so much she has an entire suite named after her in the Capri Palace Hotel.

'Very simple, lovely people,' insists Gianni.

Even Mariah Carey, famously the biggest diva in Tinseltown?

'Oh yes, a lovely lady. So nice and low-key. I arranged for her to swim in the Grotta Azzurra – with three umbrellas for privacy – just her. She loved it.'

I bet she did. But hang on a minute, isn't swimming there banned?

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'But it was Mariah Carey! And she gave me a €700 tip,' he says.

As it turns out, most of the rules here are flexible if you've got enough cash.

And of course, that's the joy of being rich - unlike the influencers and Instagrammers.

Some rely on out-of-season collaborations – free rooms, meals and boat trips in return for promotion, which Gianni insists can be helpful.

'Last week my followers went up by 500 after a collaboration with a Brazilian influencer with 18million followers!'

But most of them just pretend they're experiencing Capri's riches.

'As well as the cave and the rocks, they go to the iconic restaurants – La Fontelina, Il Riccio, to take pictures,' Gianni says. 'But they don't eat anything. Nothing! Maybe, a Diet Coke or, sometimes, a very small salad without oil.'

But back to the ring of steel and the boats. Which, from where I'm sitting, seem to be everywhere - speed boats, power boats, Sunseekers, £2million tenders for 200ft superyachts, roaring all over, trailing white foam in the deep blue sea.

Because of course it's all very well talking about restrictions and powerboat car parks and apps and fines, but someone has to enforce it all. When I ask how they police it, the mayor looks surprised.

'It is not our job. No no! We will do nothing. Not for us,' he says.

But hang on. In all the excitement I almost forgot the Grotta Azzura. Is it amazing - worth braving all the power boat waves and a three-and-a-half hour wait? Was August Kopisch right all those years ago?

Well, yes, it is pretty incredible. Huge and very blue, and all over in about three minutes flat.

But everyone seems happy. As we emerge blinking back into the sunshine, all around me heads are buried in phones, editing, adjusting, tagging and then immediately posting and declaring happily, 'That is the best post ever!'

Oh to be Mariah Carey, just this once.