He was the botanist who earned acclaim with the discovery of dozens of rare plants in his beloved Scottish isles. In the placid world of botany the name of Professor John Heslop-Harrison generated a frisson of excitement whenever it was mentioned. But doubts about the professor's work - the discovery of a rare sedge Carex bicolor and the rush Juncus capitatus on the Hebridean island of Rhum, among others - have long cast a shadow over his reputation. Now new evidence has emerged that appears to show conclusively that he faked many of his key finds.

Confidential records held by the Natural History Museum suggest that Heslop-Harrison gathered seeds during his travels and then planted them in the Hebrides. He went on to claim a series of triumphant discoveries, and to build a formidable reputation in the botanical world some 60 years ago.

When doubts about his claims emerged in a book almost a decade ago, a legion of admirers rushed to his defence. Now the author Karl Sabbagh has gained access to previous unseen records which reveal that Heslop-Harrison's own colleagues harboured doubts about his claims.

Exposure of his misdeeds may have been withheld because Heslop-Harrison, a Fellow of the Royal Society and a senior academic, was near the end of his career, and it was felt that this would be too heavy a blow to inflict on him. His son, by then also a senior botanist, had become director of the Royal Botanical Gardens at Kew.

Most of Heslop-Harrison's key discoveries centred on the island of Rúm, off the west coast of Scotland. There, in the course of a series of expeditions in the late 1940s, he claims to have stumbled on a series of rare plants, including grasses and sedges, some of them common in the Alps, but never before found as far north as the Hebrides. One spring, in a patch of grass in a glen above Kinloch Castle, a great sandstone building which dominates the island's main bay, he announced the discovery of a rare sedge known as the Carex bicolor. It was a sensational find - convincing evidence that seemed to support one of Heslop-Harrison's pet theories - that the Ice Age had never reached the islands with the result that many plants had survived.

Heslop-Harrison, who died in 1967 at the age of 86, reported further discoveries in unexpected places - on the islands of Rúm, Tiree and Coll. But one fellow botanist, John Raven, who was on Rúm when the carex bicolor was found, was immediately suspicious - it looked as if it had been recently planted, and there were no other examples of it to be found.

Raven, who found much circumstantial evidence confirming Heslop-Harrison's fakery, wrote up a report, but it lay buried in a Cambridge library until it was revealed in Sabbagh's book, A Rúm Affair. When the book was published, in 1999, senior botanists leapt to Heslop-Harrison's defence, pointing to his track record as a respected expert, and claiming the evidence against him was based on hearsay.

One of his scientist friends told Sabbagh: “Do I believe that he could or would fake discoveries? No, frankly I don't. Furthermore there was no need to. He discovered so many things, plants and insects, most have not been questioned ... Faking records or results would be a heinous sin in the eyes of any scientist.”

The evidence, which Sabbagh has now seen in the Natural History Museum, reveals that in the years after Heslop-Harrison's “discovery”, senior botanists were so concerned about his activities that they placed on record evidence confirming their belief that he was responsible for a large number of frauds. One from Dr George Taylor, Keeper of Botany at the Natural History Museum, writing in 1981, describes how he asked a fellow botanist, R.B. Cooke, who had accompanied Heslop-Harrison on many of his expeditions, to write down his own impressions of his methods.

Cooke's report gives a plant-by-plant account of many of Heslop-Harrison's “discoveries”. It is clear that Cooke had become disillusioned about the veracity of the claims.

The report states: “August 1936: I was shown a dozen or so scattered plants growing in a small piece of disturbed stony peaty ground ... I could not find a single plant of the Juncus ... apart from this piece of ground despite many hours search over ground in the vicinity which looked similar ...

“Rum: Since 1938 and up to 1946 when I was last on the island, I have failed to find Juncus capitatus except in 1943, when on the first full day of our visit I saw a dozen or more plants which in my opinion had been recently planted; there were to be seen marks which suggested a stone having been used to press in the soil round the roots.”

The final verdict on the affair comes from Cooke, who had been a good friend and colleague of Heslop-Harrison for many years. Writing to George Taylor in 1955, he said: “You may say what fools [Heslop-]Harrison must have thought us to be, or rather I should say I was. It was a very sad chapter in my life to be so taken in.”

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