Inside Thailand's last untouched island: Empty beaches, authentic villages, mangrove forests - discovering that Koh Yao Yai is like Phuket used to be 40 years ago

A tourist boom over the last three decades has turned Thailand into the busiest tourist hub in south-east Asia, with 28 million visitors piling in every year.

Which is a problem, particularly in Phang Nga Bay, near Phuket, which was so deluged with tourists that it was closed to visitors in 2018.

You can see why young backpackers are so drawn to a country which offers sun, sea, dirt-cheap-yet-excellent hostel accommodation, lively bars, party boats which cruise the islands blaring out dance music and the legendarily hedonistic Full Moon parties.

But for someone in her 50s whose private hell is a party boat, is it possible to find a corner of Thailand that hasn’t become invaded by gap year students?

Of Thailand’s 1,430 islands, you can probably only name a few. Koh Yao Yai, an island on the west coast near Phuket, is so unknown that even mainland Thais haven’t heard of it.

Soak it up: Fiona McIntosh travels to Koh Yao Yai, an island on Thailand's west coast near Phuket that is so unknown, even mainland Thais haven't heard of it. Pictured above is the island's 'showstopper' beach - Laem Haad

Fiona describes Laem Haad beach (above) as a 'long spit of bright white sand and coconut trees'

While Phuket these days is full of sparkling resorts, mega-villas and rich Russians swaddled in designer clobber, all of that changes the moment you speed away from the jetty on a bumpy boat ride across the Andaman Sea.

On the way, we pass a constellation of tiny islands covered in rainforest, with ribbons of sandy beach and few signs of life apart from wonky wooden fishermans’ cottages.

The twin islands of Koh Yao Yai and Koh Yai Noi sit side by side, separated by a narrow stretch of water. While the latter is smaller and more developed, Koh Yao Yai looks from a distance as if it’s nothing but jungle-clad hills which tumble down to the sea.

Fiona checks into Anantara Koh Yao Yai (pictured), the island's first five-star hotel

Fiona says that Anantara has 'all the trappings of five-star luxury'. Above is one of the hotel's opulent villas with rainforest showers and private plunge pool

Just 35 minutes after leaving the bustling jetty at Phuket, we arrive at the island no one has ever heard of. ‘Welcome to Koh Yao Yai,’ says our guide as we step off the boat. ‘This is what Phuket used to be like 40 years ago.’

The island is an 18-mile long, thin stretch of concentrated jungle with a smattering of small rubber and coconut tree plantations, a couple of dinky villages and some very beautiful and very empty beaches.

As the small island population is 90 per cent Muslim and many of the small restaurants and cafes don’t serve alcohol, it means the young, party crowds have given it a wide berth. Koh Yao Yai is so crime-free that it doesn’t even have its own police station. As we were told by one local, you can leave your moped by the side of the road with the keys in the ignition and it will still be there when you get back.

The hotel has been 'designed to sensitively blend into the undulating coastal landscape'

Fiona says you can visit the island's mangroves to spot native hornbills, or take a jungle hike

Until recently, accommodation options on the island were limited to a handful of cheap and mid-range hotels and self-catering villas. But this year the island welcomed its first five-star hotel, the Anantara Koh Yao Yai.

Although in some ways it is a shame progress is finally catching up with this wonderfully pristine island, the hotel has been designed to sensitively blend into the undulating coastal landscape — rather than stand out with bright lights and bling.

The resort has all the trappings of five-star luxury, from opulent villas with rainforest showers to private plunge pools, a hydrotherapy spa and vast, delicious beds that are an entirely different species to the palm mats I once slept on 30 years ago.

A buffet breakfast is served in an airy pavilion restaurant beside the free‑form swimming pool; lunch can be ordered by your sun-lounger on the sandy beach which looks out across a calm, clear sea; and in the evening you can choose to dine on local food, Japanese or a BBQ. I was also rather relieved to see that cocktails, wine and beer flow freely.

You could choose to stay put and relax at the Anantara, but that would be a great shame. Our hotel guide, Jo, took us on two rollicking excursions around the island on mountain bikes and a jeep.

We bumped along a quiet road, past farms, the odd lone water buffalo and gangs of monkeys who eye-balled us from the top of bins, past banana, palm and cashew nut trees to the island’s showstopper of a beach, Laem Haad. On this long spit of bright white sand and coconut trees, the only other people we saw were a sun-bleached French couple in their 60s, who were clearly having a wild old time on their grown-up gap year.

The hotel can also organise jungle hikes through the hinterland, kayaking through mangroves to spot native hornbills and snorkelling and scuba-diving trips to nearby islands.

It is also well worth getting a taste of traditional Thai food. Jo took us to try delicious banana-filled roti from an unassuming roadside stall, and at night we dined at local, open-air restaurant Chill Chill @ Pai where we both had a sensational Thai green curry loaded with seafood and a round of cocktails for less than £20 ($25.12).

That French couple clearly had the right idea. How wonderful to revisit the gap year experience, with all the adventure, culture and thrills of youth, but with proper beds, air-conditioning and no bugs. Even better to do it in a place still wild and naturally beautiful — and not a single party boat in sight.