The parish of Idmiston contains three villages on the river Bourne and since, the mid 20th century, Porton has been the best known because of the chemical and microbiological research station that has been there since 1916. The greater part of the airfield of Boscombe Down is in Idmiston parish although the base itself is in Amesbury parish. Boscombe Down opened in 1917 as a flying training unit. After being home to various squadrons the station was taken over by the Aeroplane and Armament Experimental Establishment that had been set up at Martlesham Heath in 1917 after its initial work at Upavon Central Flying School. The A & A E E have remained at Boscombe ever since. For much of the early 20th century most of the parish has been owned by the government to accommodate the airfield and Porton Down.
The three settlements are Gomeldon, Porton and Idmiston itself. Gomeldon is Gumela's Hill and the Saxon settlement was on the lower slopes of a hill, while Porton could derive from 'Poor' or 'Power' a possible old name for the river Bourne. Idmiston is the farm or homestead of Idmaer. This is a typical chalkland parish with arable and meadow land in the river valley and rough grazing on the downs that rise from either side of the valley. There are odd patches of clay and also substantial numbers of large flint nodules that have been used as a building material since at least Saxon times. A detached portion of the parish, Shripple, was in Middle Winterslow and was transferred to Winterslow parish in 1883.
There was substantial prehistoric settlement in this area with two large Neolithic flint mines at Easton Down and Martin's Clump, that were probably occupied for around 500 years. Bronze Age round barrows are a feature of the landscape while on Thorney Down there was a late Bronze Age farmhouse with eight outbuildings. There are several Bronze Age enclosures. During the Iron Age there were various small farms and these probably continued into the Romano-British period. On Roche Court Down there is a early 6th century Saxon cemetery with 17 graves with a further 18 graves of victims of a mass execution. It is most likely that settled Saxon occupation of the valley took place soon after this on the three village sites. By the early 10th century Glastonbury Abbey held 20 hides here and Saxon burials have been found at Gomeldon.
By the time of the Domesday Book (1086) there are three distinct communities, Idmiston being the largest with about 70-75 people, then Gomeldon with 50 to 55 and in the middle, geographically, Porton with about 30 inhabitants. Idmiston had the most land, sufficient for seven plough teams, Gomeldon had land for three plough teams and Porton enough for two. All had meadow and pastureland but only Idmiston had woodland (10 acres). Both Gomeldon and Porton had water mills. The total population was between 150 and 160.
Part of the deserted medieval village of Gomeldon, to the east of the river, has been excavated. It was originally sited on the lower slopes of Gomeldon Hill and in the early 12th century the typical long house was home to humans at one end and animals at the other. By the late 13th century/early 14th century the animals were housed in a separate building and the house, 30 feet long, was reserved for humans. Houses were of unmortared flint and set on a village street, which remains as a hollow way. By this time the houses had moved further up the great hillside and set on prepared platforms. The earliest existing building in the parish is the timber-framed Old Vicarage at Idmiston that dates from the early 15th century. It is likely that the settlement at Gomeldon was in decline by this time and in 1518 the mill is described as 'decayed' and there were only six households.
There was some rebuilding in the early 17th century beginning with Idmiston Manor for Giles Rowbach in rendered flint with limestone dressings. Around 1620 the Rectory, of brick with small flint panels, was built by John Bowle, a member of the other leading local family. During the civil war the Bowles were Royalists while another leading local family, the Redes, were Roundheads. Before the restoration General Monck was living at Idmiston Manor, he was instrumental in creating the restored constitutional monarchy. Several smaller houses were built in the early 17th century and these were mainly of timber framed construction. Four surviving ones are Thatch End in Idmiston and Box Hedge Cottage, Lane End Cottage, and Ti Trees Cottage in Porton. West Gomeldon Farmhouse was built in brick and flint.
By the early 18th century flint was again being used as the chief building material. In the early part of the century Wisteria Cottage (Porton) and Bridge Cottage (Idmiston), both considered to be houses at that time, were built of flint and are now faced with cob. Later houses were The Grange, flint with brick dressings in Idmiston, Rosemoor and Rose Cottage, brick and flint, in Porton and Dairy Farmhouse of the mid 18th century. At this time the authorities of vicar and local landowners were set against having an ale house in the parish, possibly because they felt their labourers would spend a few hours there, and so there was none. One locally famous character from this time was Moll Harris, a highwaywoman who operated from a clump of trees near Porton Village. She was caught and hanged. A more respectable inhabitant was the Rev. John Bowle (1725-1788) who was rector of Idmiston between c.1778-1788. The Rev. Bowle produced the first comprehensively annotated study of Miguel de Cervantes' El ingenioso hidalgo Don Quijote de la Mancha (known in English simply as Don Quixote). Two discrete but textually identical editions were published in 1781, one in London and the other in Salisbury. His significance as an initiator of Cervantine literary studies has been acknowledged both within Spain and internationally. He is buried in Idmiston church.
By the late 18th century there were large numbers of poor receiving out relief in the parish. There was a debate about the building of a workhouse, but it seems that this did not happen and the parish paid for its poor to live in Amesbury and Salisbury workhouses. In the late 18th century White Cottage at Porton was built of cob and around 1790 the present Birdlyme Farmhouse, of flint and a brick, was erected. Around the turn of the century a windmill of four floors was built in flint and brick at West Gomeldon.
By the early 19th century the chief crops of the parish were wheat, barley and oats, while sheep were still kept on the downs and folded on arable land to provided money for the fields. By 1848, and probably earlier, the Plough was open at Idmiston. After 1854, when the railway line was built through the parish, additional employment was provided and some local men became railway labourers. The influx of non-local labourers caused the usual problems and a rise in illegitimate births is recorded in the parish registers. A railway station was opened at Porton and a stationmaster is recorded in the 1859 Kelly's Directory of Wiltshire, while by 1855 a shopkeeper at Porton had also become a beer retailer, doubtless to serve the thirsty navvies. In 1861 Idmiston (212 people) and Porton (176) were the largest villages, while 85 people lived at Gomeldon. In 1867 the economy of the parish was still agricultural with only a blacksmith and mason, a bricklayer, a carpenter, a boot and shoemaker and the Plough at Idmiston, and a beer retailer and shop, a baker, and a grocer and draper at Porton being the only other businesses listed at that time. The fact that the shops were at Porton could be partly due to the supply line of the railway.
The early 20th century saw immense changes in this quiet parish, although things continued as normal until the First World War. Owing to the hard work of the Rev. Youngman a reading room opened in 1907 but was only for male inhabitants over the age of 14. It was open between 6.30pm and 9.30pm and took daily and weekly papers. Despite having 40 members at its peak and starting a rifle club people lost interest and the room closed in 1914.
With the use of gas warfare during the war an establishment was needed to research ways of protecting British Forces from gas and chemical weapons. 3,000 acres of land were bought by the War Department and designated the Gas Experimental Ground. Laboratories were in huts and Porton Camp was established. A meteorological section opened in 1916, while in 1917 the decision was taken to build a 24-inch (60cm) military light railway. Part of the line to the south of East Gomeldon Road was on trestle and known as the Winterbourne Trestle. There were five steam and two petrol locomotives. More land was acquired in 1918, bringing the total up to 6,196 acres, and some of this was adjacent parishes, including one over the county border in Hampshire. There were only 5, 482 acres in Idmiston parish at that time. The Headquarters building was erected in 1918 and at the end of the war Porton Camp contained 50 officers, 1,000 other ranks and 500 civilian workers.
On an agricultural note the floating of water meadows (controlled flooding of meadowland in winter to bring about earlier growth of grass for sheep) ceased in 1927. The Silver Star Bus Service was set up in the early 1930s and by 1937, when passenger traffic on the light railway ceased, had taken over most of the civilian transport to the camp. There was intensive work at the camp, by now known as the Chemical Defence Experimental Establishment (the Experimental was later dropped), on further refining the defences against gas warfare and developing effective counter measures. After the war the Microbiological Research Establishment was built off Manor Farm Road in 1949. The Porton Light Railway continued in use for freight until 1952-3.
The Memorial Hall was built in 1958 to commemorate the 37 men of the parish who fell in two world wars. Despite an increase in civilian population the railway station closed in 1968. This was in the middle of a period of substantial house building with 301 houses built between 1963 and 1973, during which time only 27 were demolished. At the end of this time Porton had increased by 49% in size, Idmiston by 65% and Gomeldon by 91%. This brought an influx of new residents, with very few families having lived here for more than a couple of generations. In 1973 30% of people had lived in the parish for less than five years and 35% had lived there for more than ten years. Playing fields were opened at Porton in 1976 and Gomeldon in 1977. In 1979 the Centre for Applied Microbiology and Research opened in a new red brick establishment and during the last quarter of the early 20th century an extremely important nature reserve has been established in Porton ranges. Attempts have been made to re-introduce the Great Bustard here. In 1991 the Establishment changed its name to the Chemical and Biological Defence Establishment to reflect its modern role more accurately.