By Iain Macdonald 

They were delivered within five days of each other in October 1981.

Two consignments of ordinary looking soil, one on the perimeter fence at the UK’s chemical weapons establishment at Porton Down in Wiltshire, the other behind a locked door on Blackpool Tower, just a stone’s throw from where Prime Minister Margaret Thatcher was presiding over the annual conference of the ruling Conservative Party.

But this was not ordinary dirt. According to the people who left the consignments there, the soil was contaminated with spores of anthrax, taken from an island off the west coast of Scotland that had been used as a deadly laboratory to design a biological bomb.

But who were the people who left them there? They called themselves Dark Harvest.

They sowed seeds of panic in the British state, were hunted by police and eventually announced the end of their campaign by the end of the year, saying they had succeeded in drawing attention to the issue.

And they have never been found.

The island in question is tiny Gruinard, uninhabited since the Highland Clearances, but overlooked by west coast communities such as Laide, Aultbea, Gairloch and Ullapool.

Its major role in history, though, was created by government action during the Second World War.

Prime Minister Winston Churchill was convinced the Germans had a biological bomb they might very well use.

So he wanted one of his own. And Gruinard, small and isolated – at least from London – but still accessible, just a mile off the west Highland coast – was the place chosen to experiment with the deadly disease anthrax.

So natives in these coastal communities watched bemused as the island was sealed off by the military and men in primitive protective gear were carried across by boat, during 1942. Sheep were shipped out to the island.

Roy McIntyre, a local businessman who served as Highland councillor for the area for many years, remembers being driven past Gruinard as a child, and spotting puffs of smoke on the island.

“It was like a few little explosions going off,” he remembers. “We wondered, what on earth is it? What are they doing there?”

What they were doing was explained years later in an extraordinary declassified Ministry of Defence film. The sheep were tethered while anthrax bombs were set off, and the smoke clouds enveloped them.

Within days the animals begin to die. Their carcasses were burnt on the island and the scientists finally left the following year, apparently satisfied their deadly experiments had worked.

Those bio-bombs were never used because the tide of war turned. But the lethal anthrax spores survived on Gruinard, making it a Forbidden Island to anybody on that coast.

Warning signs were erected, banning landings on “anthrax island” – though the word “anthrax” was not mentioned on those signs until more than 20 years later.

What we know is that livestock in neighbouring mainland communities died in mysterious circumstances in the years immediately after the Gruinard experiment, and their owners were quietly compensated by the authorities.

Nothing, though, was done to clean up the island.

Successive directors of Porton Down speculated it might even take hundreds of years for the spores to die out.

That story is told in a BBC Scotland programme due to be broadcast next week.

And what the programme makers also set out to do is to try to unmask Dark Harvest, which emerged in the 1980s, by depositing those bags of supposedly poisoned soil they said came from Gruinard at Porton Down and in Blackpool.

As it turned out, one was indeed corrupted with anthrax, one wasn’t.

Dark Harvest announced its existence – and its campaign -– in a communique to what was then the Glasgow Herald.

It claimed the group had collected 300lbs of contaminated soil from Gruinard and would be leaving sacks of it in various places across the UK, beginning with Porton Down.

“Where better to send the seeds of death,” asked the portentous statement, “than from whence they came?”

Sure enough, after first dismissing it as a hoax, the authorities found a bucket full of dirt containing anthrax spores on that Wiltshire security fence.

After a second sample appeared behind an apparently locked door in Blackpool Tower, as Mrs Thatcher’s Conservatives were meeting in the town, a Task Force was set up to investigate the mystery identity of Dark Harvest.

People in the area were again bemused onlookers, as military police and Special Branch dug away at Dark Harvest, though this time under the intent gaze of the media. Among those involved in the investigation was then Detective Inspector Colin Macdonald, himself from the west coast islands. But even he found a wall of silence.

“People didn’t want to say anything,” he remembers, “in case they said too much.”

At the end of that year, another statement emerged from Dark Harvest, this time pinned to the doors of the Scottish Office in Edinburgh. It announced the group had achieved its objective in drawing attention to the poisoned island. It would take no further action, it declared – for now.

And with that, Dark Harvest disappeared.

But it had indeed achieved its objective. In 1986, Gruinard was again invaded by the men in white coats, who treated the island with a Heath Robinson sprinkler system, using water and formaldehyde to cleanse the soil.

Subsequently, a government minister braved a wet and windy day on the water to declare Gruinard clean and take down the warning signs. I was one of the media party that accompanied him. Back then, I worked for the BBC as a journalist with the Inverness-based Radio Highland. Broadcasting across the Highlands and Islands, we thought we were as well placed as anyone else – well, maybe not Special Branch - to track down Dark Harvest.

The Highlands in the 1980s were a more radical place than might have been assumed by those who lived elsewhere, so we reckoned we had no shortage of “suspects”.

People who might have featured on that list included an alternative off-grid community on the coast at Scoraig.

The remarkable Kay Matheson, who lived and taught in the area and was one of those who stole the Stone of Destiny from Westminster Abbey.

There was also the equally remarkable Jean Urquhart, who ran the Ceilidh Place bar and bunkhouse in Ullapool and set up the area’s CND branch.

There was also the Wester Ross-born nationalist lawyer Willie Macrae, who was to die of a bullet wound at a Highland roadside in 1985.

A petition was started in Laide by local man John Alick McRae and, before Dark Harvest, he had been a lone voice in the wilderness, appearing on our wavelengths urging a clean-up of the poisoned island, when nobody else was taking much notice.

Declassified documents revealed in the years since indicate he was indeed a police suspect. He denies it, as do the others I have named, or at least those still able to do so.

The programme investigates all of these possibilities, as we did. We never solved the mystery of Dark Harvest. Does this programme? You will have to watch it to find out.

The story – the scandal – of Gruinard may have been forgotten by many.

But it raises a whole series of questions about what happens behind the scenic scenes in the Highlands and Islands, and indeed the way the area is treated by government, that are still being asked today.

Programme maker John McLaverty says it’s fascinating. “Gruinard Bay is a stunning place to film in, and nowadays filled with camper vans winding their way around North Coast 500,” he says.

“The brochures will tell you it’s a quiet and peaceful place. But if the scenery could speak, it would tell a very different tale.”

The programme he has made tells that tale.

And here’s a final thought. The first Dark Harvest communique claimed the group removed 300lbs of contaminated soil from “anthrax island”. Most of that was never used.

So, if that claim was true, is it still around somewhere in the Highlands? Only the so-called commandos of Dark Harvest know the answer to that.

l The Mystery Of Anthrax Island is on BBC Scotland on Tuesday at 10pm.