The Robinson Crusoe experience (with solar panels)

Fleeing the crowds, heat and fumes of Zanzibar city, Adrian Mourby and his wife find refuge on Chumbe, an eco-friendly coral island off the coast

Zanzibar is crowded and hot. Sailors used to claim they could smell the fabled Isle of Spices long before it appeared over the horizon but all I was getting was an unpleasant cocktail of frangipani, exhaust fumes and dead fish. The marketplace looked like an abattoir and the drains were on strike. So was my American wife Kate, who was steadfastly keeping to our hotel, lapping up the air conditioning and agreeing whole-heartedly with the opinion of David Livingstone, who dubbed this island "Stinkibar".

Zanzibar is crowded and hot. Sailors used to claim they could smell the fabled Isle of Spices long before it appeared over the horizon but all I was getting was an unpleasant cocktail of frangipani, exhaust fumes and dead fish. The marketplace looked like an abattoir and the drains were on strike. So was my American wife Kate, who was steadfastly keeping to our hotel, lapping up the air conditioning and agreeing whole-heartedly with the opinion of David Livingstone, who dubbed this island "Stinkibar".

And the worst of it was we were not due to leave for another two days. Fortunately, an old toothless Portuguese in the hotel bar thought he had the answer. "Chumbe," he said. "It's only eight miles off the coast. You British built a lighthouse there. It's a small island, uninhabited and has 90 per cent of all the coral reef in East Africa."

"Yes!" said Kate in exaggerated delight. "I so need a coral island."

As a child my wife had been obsessed with Robinson Crusoe. This sounded much more like the kind of Indian Ocean experience she was looking for. As for me, I was happy enough to leave the humid alleyways of Zanzibar city and play at castaways. The old man said it would take less than half an hour by boat. All we had to do was get a taxi down to the mangrove swamp at Mbweni Ruins.

Mbweni turned out to be the ruins of a school for freed slave girls, another thing we British built in the 19th century. In the 1970s it was the No.1 place for European raves in Africa. Now it's all fenced off, but there's a small damp hotel nearby from which you can take a boat out to Chumbe and here we found Karen, our coral island ranger.

Unfortunately, Karen had misread the tide table so we ended up slopping out to the boat through mangrove swamps, ankle deep in lukewarm water and narrowly avoiding stepping on bright red starfish and some vicious-looking sea urchins. My wife described them as "pompoms with attitude". The boat was long, old and low, with a canvas awning to keep the sun off.

As we puttered west Karen pointed out broad-sailed dhows, circling Chumbe. These were Zanzibari fishermen. They are allowed to fish freely off the west side of the island, but can't come closer than 400 metres on the east. As we drew closer to Chumbe we could see why. The island's fragile corals are vulnerably visible in this shallow sea, only a metre or so below the surface.

The island itself is long and thin and dense with its own unique foliage. It looked for all the world like a coral birthday cake topped with a stubby white lighthouse candle.

We stepped off into warm water and squelched our way up the beach. Ahead lay the ruins of what turned out to be a one-man mosque which was built for the lighthouse-keeper, and a large open-sided and palm-thatched building that used to be his house but was now the hotel-cum-visitor centre.

Karen promised us an underwater safari after lunch, but first she had to deliver supplies to the hotel. Chumbe, whose area totals only one square kilometre, is wholly dependent on the mainland for everything from food and water to writing paper and torch batteries. While Francis, the manager, took stock we took lunch on a makeshift table facing the ocean. Our furniture looked as if it had been salvaged from a shipwreck and augmented with bits of designer driftwood. Chumbe, I soon realised, is seriously green.

We ate grilled kingfish, salad and vegetables but left the big bowl of chips, which I fear had been ferried over specially for us. Afterwards, Francis brought us slices of mango and paw-paw for dessert. He then escorted us to our "bungalow". Even though we were only there for the day, the fare over included lunch and use of our very own thatched hideaway along the shore. Here we could rest, change and shower off the seawater.

The bungalow lay down a sandy path that was criss-crossed by hermit crabs scurrying sideways into their burrows as if rush hour had suddenly descended. My wife loved the bungalows. They were two storeys high, with huge curving roofs - like those at the Sydney Opera House - to catch rainwater.

Chumbe has no well or spring, so its reliance on rainwater for washing and bathing is total. Bottled water is provided for drinking and cooking but the "grey" water from each sink and shower gets filtered and used to water the plant beds in front of the bungalows. According to Francis, new plants have been specially introduced that have an ability to absorb the phosphates and nitrates in the used water. The beds are encased in clay, ensuring that no used water runs into the natural environment. It was all very well thought out and made Robinson Crusoe look like a complete amateur.

Solar panelling provided each bungalow with its light and water heating, but Kate wanted to know where the air conditioning was. "From the sea!" Francis laughed, and indeed we could now see that our bungalow was completely open on the ground floor with dense foliage affording what privacy we felt we needed. We changed happily for our swim but when it came time to use the "compost" lavatory Kate was less than happy. She still remembered the long-drop privies that haunted her through many years of American summer camps. The sign said three scoops of earth on top were every bit as effective as a flush. "Huh," said Kate, peering down in disgust. "Well they're not as bad as those fly-ridden thunderboxes."

Our snorkel safari was good, with lionfish rather than lions, and schools of chocolate-dipped chromis instead of the ubiquitous herds of wildebeest that we'd seen on the mainland. I was saddened to see how much coral had been broken off in recent storms. It did look as if someone had been down there with a baseball bat.

As we surfaced and made for the beachside communal showers we saw a party of Zanzibari schoolgirls emerging from the forest in their pleated skirts and starched white shirts. They'd been over for a day to learn about the environment. In fact, the $70 (£36) each that we'd paid subsidises such trips from the mainland.

Francis greeted us cheerfully and asked if we'd enjoyed our swim. He even said we could stay the night if we wished as the bungalow was ours till tomorrow. We both wished we could have stayed. It would have been very romantic to sleep under the stars and listen to the sea breaking quietly on he beach. Instead, I contented myself with a brief swing in a hammock until it was time to go back. My wife, being far more energetic, went to explore the island with one of the rangers.

Chumbe is covered with dense coral rag forest and has its own indigenous fauna: a species of tiny and very edible deer that got marooned here when sea levels rose and which is now all but extinct on the mainland; and the huge coconut crab which has had the great misfortune to be credited with aphrodisiac qualities and is now understandably shy of humans. Kate found neither but did get the chance to climb the lighthouse and watch fishing dhows in the distance heading back to Zanzibar.

We left with some sadness, having really under-stayed our welcome. "That was everything I could have asked for from a desert island," said Kate wistfully. "Except for proper plumbing."

GIVE ME THE FACTS

How to get there

The writer travelled as a guest of Rainbow Tours (020-7226 1004; www.rainbowtours.co.uk), which offers a seven-day holiday in Zanzibar from £1,045 per person, based on two sharing. The price includes return flights from London Heathrow to Zanzibar via Dar es Salaam, private transfers, three nights' accommodation at Breezes Beach Club on a half-board basis, two nights at Chumbe Island Lodge on full-board basis, and one night's b&b accommodation at Tembo House in Stone Town.

Further information

Go to www.chumbeisland.com.