Visitors to the Isles of Scilly, about 30 miles off the Cornish coast, are not allowed to bring cars, so these walkable, flowering islands are one of the UK’s ultimate car-free destinations. A new Ocean Scilly Festival in late August will offer rock-pooling, gig racing, shipwreck tours and the chance to kayak to an uninhabited island. Today, as I wander the sandy coast path of Tresco with my husband, the tranquil island feels like paradise. In the evening light, stately pines, tree ferns and wine palms sprout from a jungle of pink-flowered geraniums. But getting here has been a turbulent nautical adventure. And last week, a planned fast ferry service was axed before carrying a single fare-paying passenger. Storms fall in full fury on England’s westernmost extremities. Our sailing on the Scillonian III from Penzance to St Mary’s was cancelled “due to a deterioration in the weather forecast and strong winds”. With train tickets booked months ago, we decided to head to Penzance anyway. There are worse places to be marooned. We strolled along the wave-battered seafront to Newlyn to eat grilled hake with samphire and capers (£9.75) at the riverside Mackerel Sky. Then we hopped on the frequent minibus to Mousehole for a stroll round the twice-weekly craft fair and ended with a pint in the Dolphin Tavern, watching storm-tossed boats in the nearby harbour. The next day’s sailing was delayed by wind and tide. But we finally see-sawed past the Cornish coast into a wild seascape, where huge angular gannets and sleek dark guillemots dived into boiling surf and blue-green brine. According to the conservation charity Orca, the Scillonian boasts the most diverse wildlife-spotting opportunities of any UK ferry route. We see-sawed past the Cornish coast into a wild seascape, where huge angular gannets and sleek dark guillemots dived Several boats ferry locals and visitors around the archipelago. We cross on a blue and white boat from St Mary’s, the main island, to Tresco (£7) . One of a handful of island vehicles meets the boat to help visitors with luggage. Tresco has a smart new fleet of zero-emission electric buses. The next morning is misty, making the spectacular Tresco Abbey Gardens even more atmospheric. Warmed by the Gulf Stream and sheltered by nine-metre hedges of evergreen oak, the tropical garden flourishes year-round and has done for more than two centuries. Augustus Smith, banker, botanist and later Liberal MP for Truro, bought the Isles of Scilly from the Duchy of Cornwall in 1834. Rather than build a house on the largest island, St Mary’s, Smith chose to live on secluded Tresco and grow what would become the Abbey Gardens (£18/£5 adult/child). The other islands were later returned to the Duchy, but Tresco is still privately owned by the same family. Red squirrels are nibbling hazelnuts and chasing each other round the trunk of a Monterey pine. Along a bamboo-bordered path, we find Augustus Smith’s collection of figureheads, salvaged from local wrecks, looming eerily out of the fog. Proteas are blooming flamboyantly pink and orange among surreally tall palms near the ruined, plant-covered arch of an old Benedictine priory. There are towering blue spires of echium, yellow tree dandelions, birds-of-paradise and scarlet bellflowers. We bump into Andrew Lawson, Tresco’s head gardener for nearly 40 years, who tells us 287 species were already flowering on New Year’s Day. In the afternoon, when the tide is low enough, we walk between Tresco and the neighbouring island of Bryher and back again. The weather meant yesterday’s Low Tide festival was cancelled. But there are roughly 30 walkable tides as well as twice-yearly pop-up parties to celebrate (the next Low Tide festival is on 19 September, and Scillonian is offering 10% off fares from Penzance (use code TASC24). As water deserts the seabed, it exposes a hidden world. There are ridged cockles and scallops, whelks and winkles Gabby and Trevor Williams from Truro and their dogs Obi and Rae are among those making the crossing today. They’ve come well equipped with waterproof shoes, shorts and a change of clothes in a rucksack. What will they do on the other side? “Have another walk, have a drink in the pub, get the boat back,” says Trevor cheerfully as they splash through the shallows. A tiny pilgrim-trail of people, “like a line of ants,” as one Bryher resident puts it, can be seen making their way across distant sandbanks. As water deserts the seabed, it exposes a hidden world. There are ridged cockles and scallops, whelks and winkles. I walk between beached bundles of seaweed, marvelling at the colours and textures: thick amber sea ribbons, frondy gutweed, tender lime-green laver, wrinkled sugar kelp, pimply bladderwrack. Stranded along with these underwater forests are small mud-coloured shore crabs and seven-armed coral-pink starfish. We’re staying at Tresco’s tasteful New Inn, with its recently renovated rooms and wood burner in the guest lounge (doubles from £221 B&B including entry to the spa and gardens). Next day, we relocate by boat to the spacious art-filled Hell Bay hotel (doubles from £135 B&B) on the wilder isle of Bryher. The island also has a campsite (£13pp). Hell Bay serves picture-perfect plates of food and one of the best views I’ve ever seen. Our bedroom looks past palm trees to an ever-changing seascape and numerous tiny islands: Horse Rock, Seal Rock, Buzza, Merrick, Cuckoo, Illiswilgig … The only sounds are roaring waves and birds from both beach and garden: blackbird and wren, herring gull and oystercatcher. Bryher may be the smallest of the five inhabited Scilly isles, but there is plenty to see. It is less than five miles round, but it takes us all day to explore each sandy cove and grassy headland, cafe and honesty store. There’s an extraordinary contrast between the wild salt-lashed Atlantic coast, facing west and the peaceful flower-fringed channel towards Tresco. There are wildflowers everywhere, mostly supersized tropical garden escapees: Bermuda buttercups, African daisies, fleshy-leaved sour figs and succulent aeoniums covering old stone walls in huge emerald rosettes with pyramids of bright yellow flowers. The only sounds are roaring waves and birds from both beach and garden: blackbird and wren, herring gull and oystercatcher As we climb through the cairns over windy Shipman Head at the north end of Bryher, the rabbit-cropped green underfoot is a dense mat of lichens, stonecrops, scurvygrass, thrift and heather. Dropping down towards The Town, as the scattered hamlet round the quay is known, we pass campions and bluebells, fields of naturalised narcissi, primroses, celandines and endless oniony banks of white-flowered leeks. Passing the harbour, there’s the haunting call of a curlew and a seal swimming near the beach. As we sail back next day on the Scillonian, it’s calm and sunny. A dolphin arcs through the waves nearby and hundreds of seabirds fly past us, heading west as if chasing the setting sun. From Penzance, we’re catching the Night Riviera – something I’ve never done before although I’ve made dozens of trips to Cornwall (basic fare £55, cabins from £34 extra including breakfast). The snug cabin has barely room for the two of us to stand simultaneously. But the bunks are surprisingly comfortable and the train runs smoothly to London, where we wake to tea, pastries and pavements rocking gently up and down.