Long before the end of his life he had become a treasured Suffolk institution. He was honoured in 1996 by appointment as MBE for services to nature conservation, and by a Rivis vice-presidency, the highest accolade bestowed by the Suffolk Naturalist Society, of which he was an active member over 70 years.

In his youth, he joined the small staff of Ipswich Museum where, given his already considerable expertise in wild plants and photography, he was put in charge of natural- history exhibits, including the herbarium. There he remained until retirement in 1977.

His first contribution to the Transactions of the Suffolk Naturalists' Trust on "Missing, Doubtful, New or Otherwise Interesting Flora" in 1934 was followed by a stream of others, equally interesting and often entertaining, written in a slightly florid, mannered style in imitation of the journal's editor, the entomologist Claude Morley (who also wrote poetry under the pseudonym Maude Clorley).

By the time Simpson's Flora of Suffolk was published in 1982, Simpson knew his county and its plants as few have ever done before or since. The work of half a century of patient recording, it drew on other surveys, but was mainly Simpson's own work, a fact recognised by the Suffolk Naturalists' Society who published the work and insisted it be called Simpson's Flora.

The Flora includes 285 of the author's splendid colour photographs of flowers in their natural setting, included at Simpson's insistence, and for which he re-mortgaged his house to cover the extra costs. Among the records of plants, places and local lore are glimpses of his unusual dedication. Worried that a colony of sea-holly growing close to a path would end up in someone's garden, he "successfully guarded it by sitting near the plants for several weekends". He added, "I can usually identify vandals, even at a distance." He also feared that deadly nightshade might be threatened by over-zealous safety officials, and so: "Where possible, I visit the sites and remove the berries."

While recording flowers in 1938, Simpson discovered that a small meadow famous for its purple, pink and white fritillary lilies was in the process of being drained and ploughed. He dashed off a characteristic letter to the East Anglian Daily Times, warning that the countryside is rapidly becoming less floriferous in this mechanical and destructive age, and naturalists must defend the heritage of beautiful wild flowers, unless our future flora is to comprise only aliens and weeds.

An appeal raised £75, enough to purchase the small field for the Society for the Promotion of Nature Reserves. Mickfield Meadow was among the first formal nature reserves, described today as a bewitching place, an oasis of meadow flowers in the midst of a vast arable desert.

Towards the end of his life, Simpson bought a small area of coastal marsh on the Ore noted for its colony of the sea pea and other rare plants, and presented it to the Suffolk Wildlife Trust. Described as "a wonderfully lonely spot with an aura of timelessness", it is known as Simpson's Saltings.

He believed, with some passion, that the business of nature conservation was to buy as many good sites as possible, and thereafter leave them alone. Though a member of many conservation bodies, he regarded many of their activities as a waste of time, if not actually harmful.

A confirmed bachelor, Francis Simpson lived in Ipswich, in a modest house with a garden in which wild flowers, some of them transplanted from threatened sites, were left to run riot. Gardening, which he regarded as cosseting, was reserved for his collection of double begonias in the greenhouse. Fortunately he remained remarkably fit almost to the end of his life. As his friend Eric Parsons said of him, "Nothing but infirmity will stand between Francis Simpson and the Suffolk countryside when a fine day dawns. Be assured he will be out".