The Shiants' name comes from the Gaelic Na h-Eileanan Seunta meaning "Enchanted Islands". This privately owned group of about 12 rocky islands and skerries lies in the Minch, some eight kilometres east of Lewis, 35 kilometres from the mainland, and 20 kilometres from the north end of Skye. There are three principal islands. The largest is Garbh Eilean (Rough Island), which is connected by a shingle isthmus to Eilean an Tigh (House Island). The separate Eilean Mhuire (Mary’s Island) lies a few hundred metres east across the Bay of Shiant. All three of these islands cover no more than 143 hectares and have been uninhabited for many years, although the bothy on Eilean an Tigh is used by the owners and visiting naturalists.

I CROSSED to the Shiants in a fast inflatable from Harris. My skipper Seamus had made the trip many times, but delighted in telling me the story of the Blue Men (Na Fir Ghorma in Gaelic). These blue-skinned mythological creatures take human form and inhabit the waters of the Minch, raising storms and wrecking ships. Sometimes the chief of the Blue Men will challenge the skipper of a passing boat to a rhyming competition. If the skipper fails to finish a couplet, he and his ship are doomed.

As we approached the biggest island, I was struck by the scale of the cliffs on Garbh Eilean. Consisting of columnar basalt pillars, they are similar to the rocks of Staffa, but are much higher, rising sheer out of the sea to over 120 metres. When geologist and traveller John MacCulloch visited the Shiants in 1819 he was also mightily impressed: "They exceed them [the cliffs of Staffa] in simplicity, in grandeur, in depth of shadow, and in that repose which is essential to the great style in landscape." And just like Staffa, there are fabulous sea caves and arches in the cliffs. As MacCulloch pointed out: "The lover of picturesque beauty will ... be gratified with a display of maritime scenery."

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As I stared at the great cliff, watching a pair of sea eagles soar into the dizzying void above my head, Seamus played a traditional tune on his sound system: a Gaelic song Ailein Duinn or "Dark-Haired Alan", which tells the doleful tale of two lovers. Alan was a sea captain from Lewis and was betrothed to the love of his life, the young and beautiful Annie Campbell. In the spring of 1788, Alan set sail from Stornoway to the island of Scalpay, where the happy couple were to be married. Tragically, Alan never reached his destination. A violent storm caught his ship and dashed it onto the rocks with the loss of all hands. Alan’s body drifted in the tide until it reached the Shiants. When his bride-to-be heard news of his drowning, she wrote the lament for her lover: Ailein Duinn. Knowing that she would never feel his arms around her again, Annie pined away. But that’s not the end of the story. The boat that later took Annie’s coffin to the burial ground was also struck by a storm and her coffin fell into the sea. Carried by swirling currents, it reached the Shiants and landed at the exact same spot where Alan’s body had been washed ashore. There on the pebble beach between Garbh Eilean and Eilean an Tigh, the two lovers were reunited in death.

Seamus steered us through a natural rock arch and then anchored in the bay, letting me use a dinghy to make my own way ashore. The cliffs all around were teeming with noisy, raucous life. Thousands of sea fowl crowded on the ledges or floated on the guano-splashed water where feathers drifted in the tide. Overhead, the sky pulsated with dark, swirling flocks of shrieking seabirds: puffins, razorbills, guillemots, kittiwakes and innumerable gulls of different varieties. The Shiants are home to one of the biggest and most important breeding colonies of seabirds anywhere in Europe.

It’s a veritable seabird city, where every spring an estimated half-a-million birds arrive to nest, hatch their eggs and rear their young.

Sadly, the numbers that throng the cliffs have been steadily declining over the years. Various theories have been put forward to explain why, from global warming to pollution, but there is one explanation that seems as undeniable as it’s unpalatable: rats – an estimated 3,000 of them. The rats are Rattus rattus – the black plague rats that originated long ago in South East Asia. No-one knows when the rats arrived on the Shiants but it’s likely that their ancestors escaped from one of the many ships that were wrecked on the islands over the centuries. Perversely, because black rats are actually very rare in Britain and certainly rarer than the seabirds they kill, they are considered to be a protected species. Until recently, a natural balance existed between the numbers of rats and seabirds. Although rats attack and eat nesting birds, the bird colony was never destroyed because in winter, after the birds have left, the rats have no food supply and many die of starvation. However, because the birds have suffered severe food shortages in recent years, their numbers have declined dramatically. This is why, controversially, there is now a campaign to eradicate the rats completely.

Although the rats might have flourished on the Shiants, the permanent population of humans left long ago, ending a history of habitation that’s generations deep. The original Iron Age settlers tilled the land and lived off fish and seabirds. The Vikings knew the islands well, stopping off on their way up and down the Minch. Celtic monks built a place of worship 1,400 years ago on Eilean Mhuire.

By the beginning of the 20th century, the Shiants were only sporadically inhabited by seasonal shepherds and passing fishermen, but in 1925 the novelist Compton Mackenzie bought the islands and restored the old shepherd’s bothy as a writer’s retreat. Best known today for his books Whisky Galore and Monarch Of The Glen, Edward Montague Compton Mackenzie was a colourful, extrovert character, born in England to a theatrical family. During the First World War he was recruited by British intelligence and operated as a spy in the eastern Mediterranean. Although he was born English and spoke with the cut-glass tones of the English aristocracy, Compton Mackenzie had a Scottish soul. He immersed himself in Scottish culture and became a founder member of the SNP.

Mackenzie loved islands almost as much as he loved Scotland. In fact, he collected them. After living on various islands in the Mediterranean and the English Channel, he bought the Shiants in order to get closer to his Scottish roots; and it was in the bothy on Eilean an Tigh that he was inspired to write a two-volume novel called The North Wind Of Love. Set on an island, it tells the story of an author, uncannily similar to Compton Mackenzie, who builds a house, and dreams about an independent Scotland. Sadly, a decade later, and with his dream still unrealised, financial worries forced Mackenzie to sell up and move on – eventually settling on another island further to the west: Barra. However, the Shiants’ literary connections didn’t end there. The islands were purchased by the publisher Nigel Nicolson – son of the controversial and flamboyant author Vita Sackville-West, whose lesbian love affairs had scandalised society in the 1920s and 1930s. The Shiants are still in the care of the Nicolson family, and the author and broadcaster Adam Nicolson has written extensively about the islands, which he loves with a passion.

Extracted from The Hebrides by Paul Murton. The book is published this Thursday (August 10, 2017) by Birlinn (£14.99, paperback)

About the author: Paul Murton is a broadcaster, film-maker and historian. He is the presenter of BBC TV's Grand Tours Of The Scottish Islands