The curious German island that Britain swapped for Zanzibar

Heligoland has been under the sovereignty of the Danes, the Germans and the British at various points in history – Martin ElsenGulls bickered on the cliffs. A red sea-stack stood tall, like the finger of a subterranean giant. A small sightseeing plane circled overhead in the cloudless sky.

I had nearly completed my morning lap of Heligoland, an island so small you can walk the whole thing in an hour. Looking out to Düne, its even smaller neighbouring island, I tried to imagine how different this scene would have looked if 100 or so people had ticked "Yes" instead of "No" on their ballot papers 15 years ago.

In 2011, the people of Germany's only offshore island were asked a question in a referendum: should they bet big on tourism by building a land bridge to little Düne, adding 1,000 hotel beds, new homes and a theme park?

The red sea stack, known as Lange Anna, on Heligoland – Brigitte Rauch

They voted against the expansion by a margin of 55 to 45 per cent. Fifteen years on, I visited this North Sea outpost, once owned by Britain, to find out whether it was the right move. The topic, it transpired, is anything but settled.

Shortly after arriving in Heligoland, I entered a little orange hut beside the museum. Inside, I found Heligoland's artist-in-residence, Johann Wieghardt, who was halfway through a painting of the island's cratered landscape.

"I have been overwhelmed by the heavy history of the island," he said, flicking his small brush along the canvas. "But the way nature and humans have rebuilt Heligoland, it's uplifting."

Through the years, Heligoland has been under the sovereignty of the Danes, the Germans and the British. During British rule, which began in 1807, the island was invariably described as the "Gibraltar of the North Sea" for its strategic shipping and naval significance.

On August 8 1890, the people of Heligoland woke up as British citizens and went to sleep as Germans. As part of this handover, Germany ceded Zanzibar to the British crown.

In the decades that followed, Heligoland (now called "Helgoland" in German) continued to flourish as a holiday resort. Today, walking the promenade, where visitors eat lobster rolls and drink rosé on hotel balconies, that idyllic spirit endures.

The island was particularly popular among artists, intellectuals and radical thinkers. It was in Heligoland, in 1925, that the scientist Werner Heisenberg made a breakthrough in his theory of quantum mechanics.

Heligoland is a popular tourism destination – Alamy

However, during the Second World War, the Nazis decided to build a major naval base on the island. If there are multiple universes, this decision set Heligoland on the path of a new, fatal reality.

On a quiet residential street in Heligoland's upper level, or "Oberland", I walked down some steps that could be mistaken for the entrance to a public lavatory. Through a locked door, I descended a network of air raid bunkers, threading deep beneath Heligoland's rocky mass like arteries.

On April 18 1945, the people of Heligoland hurried to these tunnels with just one small bag of belongings each. Nearly 3,000 people huddled inside, sitting on their designated benches in eerie silence. Above, 981 British planes dropped 7,000 bombs on the island through the course of that day.

"You could not recognise anything," said one islander, describing the moment he emerged from the bunkers. "Bomb craters and smoke, ruins and a few solitary chimneys. A completely different, terrifying world."

The island was riddled with craters and ruins during the Second World War – Corbis Historical/Hulton Deutsch

Another day of reckoning came precisely two years later. During Operation Big Bang, the British military placed 7,400 tons of surplus ammunition across the island to destroy Germany's military outpost once and for all.

From the mainland, 35 miles away, some exiled residents saw the white flash and watched as a mushroom cloud shot miles into the sky, followed by an almighty blast. This was the biggest single-explosive detonation in history. Many feared that, once the dust settled, there would be no Heligoland left at all.

I took the short boat ride across choppy waters to Düne, where I met ranger and seal warden Michael Janssen. He looked the part with his three-pronged goatee and safari hat.

We walked around the island, sidestepping sea kelp on the white-sand beaches, watching our feet for rare red flint pebbles. He stopped by the island's airstrip, a relic of Heligoland's wartime past, which is still used by sightseeing planes (last year, the scheduled service to the mainland was discontinued). Here, Janssen has to handle a particularly unusual part of his job.

"This fence is supposed to stop the seals from getting on to the runway," he said, showing me how they place their flippers on the top and then flop themselves over. "Getting them back to the beach can be a challenge."

Greg Dickinson with seal warden Michael Janssen – Greg Dickinson

Düne is a contradictory place. It feels so peaceful, so wild, and yet it would not exist were it not for the Nazis, who expanded the island's landmass tenfold during the Second World War. Today it is seen as a retreat by the islanders, with its campsite and colourful little bungalow rentals. For all there is to be gained, many believe something would be lost if that land bridge were ever built. And that prospect remains firmly on the table.

"The referendum ripped apart families," said Katharina Schlicht, the Heligoland tourism director, who I met by the pastel-coloured Scandi-style huts on the harbour front.

Despite it being the end of September, people wore T-shirts and shorts thanks to the temperate jet-stream climate. I saw more than one visitor lying on the ground, perfectly still, with a lens the size of a walking stick, hoping to snap one of the island's "big five" migratory birds.

"In summer, the supermarket is very full and you have a lot of variety of foods," Katharina said, an example of how tourism is the lifeblood of the island. "In winter? No."

The island is notably different from other holiday spots: there are very few vehicles and many businesses only accept cash

We looked out to the pier, where the FRS Helgoline catamaran waited to load up its return passengers. The latest challenge for the authorities is that Heligoland's harbour facilities and landing pier are in need of urgent repairs, but the island receives little public funding to support such projects.

In total, the repairs would cost in the region of €500m (£420m). Private investors have offered to bankroll the repairs if the controversial sand-replenishment project were to get the green light. Another referendum, which threatens to drive a new wedge between older and younger generations, could be the only way forward.

"I see no other solution at the moment," mayor Thorsten Pollmann told a town-hall meeting in May, stressing that he was personally torn on the subject of reunifying the two islands. But times, he said, had changed.

The referendum could occur as soon as this winter, but change won't come quickly. A phrase I heard more than once during my weekend on the island was: "On Heligoland, the clocks move differently."

Heligoland moves to the beat of its own drum. Literally, in the case of the oompah band that marched triumphantly towards the island's annual Oktoberfest event during my stay. It was a riotous evening, although some locals boycotted the event on the principle that it is a southern, not northern, German tradition.

In some ways, there is a sense of being stuck in time: Airbnb does not exist on the island. There are no cars, except for a handful of electric emergency vehicles and buggies. In some establishments, cash remains the only form of payment.

The island remains car-free, making for a genuine sense of escape – iStockphoto

Uniquely for a tourist destination, many tour guides cannot speak English, and information signs are written in German only. A few English loanwords have entered the island's Halunder dialect, which is still spoken by 50 or so residents. Eavesdrop on the right conversation and you might hear words that sound like "boat" or "grog". Fitting, given that many visitors board the return boat with copious amounts of duty-free booze.

As my ferry drifted into the North Sea, and the red-and-white radio tower dipped out of sight, I was caught in two minds. You desperately hope this most curious island keeps its slow and spirited charm. And yet you also wish it to be in a position to thrive in the future. The question, like one of Heisenberg's quantum conundrums, is whether Heligoland can exist in both states at once.

From the UK, fly to Hamburg and then board the FRS Helgoline to Heligoland. This service, which takes around three and a half hours, departs Hamburg early in the morning and returns from Heligoland late afternoon from March to October (from €99 return). Through the winter, a slower ferry service operates from Cuxhaven (cassen-eils.de).

Greg Dickinson stayed at the four-star Strandhotel (doubles from €150) on Heligoland. In Hamburg, the best hotel for the ferry is the Hotel Hafen Hamburg (doubles from £124). For more information about the island visit heligoland.de.

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