It is a national nature reserve and Site of Special Scientific Interest owned and managed by the Forestry Commission.

In Roman times it was an iron smelting centre, during the medieval period it was in the Royal Forest of Rockingham, and later it became part of the estates of the Duke of Bedford.

[6] There were 462 species of vascular plants listed as present in the woods in 1975,[7] and the whole range of flora associated with ancient woodland is exceptionally rich.

Although there is now no doubt that the non-native conifers damage and diminish the conservation value of the woodland, it appears that in this instance they also secured its survival.

This is not ancient wood, but a 19th-century conifer plantation, which was replanted in the 1950s with beech, Norway spruce, Western hemlock and Grand fir.

Instigated by G.F. Peterken of the Nature Conservancy Council, it included contributions from the Forestry Commission, the Institute of Terrestrial Ecology and the local Naturalist Trusts.

[16] Acknowledging the role commercial demands had played in enabling the continued existence of the woods, Peterken states: The fate of the woodland on the present site of Bedford Purlieus in Roman times is unknown.

A reasonable conjecture is that the local iron-smelting activity, needing a supply of fuel, obliged the Romans to retain woodland in an area of relatively dense settlement from which it would otherwise have been cleared.

It is a curious co-incidence that 2000 years later, its survival as a native broadleaf woodland was ensured through a period of intensive coniferous reforestation by the renewed demand for iron ore.[17]During the 1970s the Forestry Commission had begun a shift in focus to conservation and amenity value of their woods.

This has facilitated the Forestry Commission to re-instate areas of coppicing, open up grassland glades and remove conifers and other introduced species.

[21] He went on to be created Earl of Bedford by Henry VIII and was granted a vast estate at Woburn Abbey by Edward VI.

Six generations later, William Russell, the 5th Earl (who would later become Duke of Bedford) was required by Charles I to pay £200 to 'Dissaforest' (sic) his woods at Thornhaugh.

The King needed money to fight the English Civil War, and this was one of many ways the Treasury found to raise it.

[23] The Charter of 8 August 1639 sets out definitively that the woods are now purlieus, that is, land that was once part of a Royal Forest but has been legally disafforested.

It names the various compartments (or sales) that make up the woods, and affirms that, "for £200 of lawful money of England well and truly paid" the 1,648 acres are "altogether dissaforested".

It goes on to explain: The Earl of Bedford can keep dogs not expeditated,[a] hounds, greyhounds and beagles, Netts guns Bows and arrows and all other engines to take chase and drive all wild beasts and birds of any kind and at all times of year hereafter for ever to fell and cut down all and all manner of woods underwoods coppices and trees as well oaks as other trees great and small whether green or dry of what nature or kind whatsoever being or to be within or upon.

The estate was bought by William Wentworth-Fitzwilliam, 7th Earl Fitzwilliam,[31] a young man who had inherited a vast fortune from his grandfather two years previously.

[32] However, only nine years later the Bedford Purlieus were sold on, this time to a timber merchant, who it is thought felled all the saleable trees.

It was an heiress of the Semarc lands who, in the 15th century brought the woods to the Russell family, Earls, and later Dukes of Bedford.

[2] The first archaeological excavations were carried out by Edmund Tyrell Artis (1789–1847), the Steward of the nearby FitzWilliam estate, in the first half of the 19th century.

With both available on one site, this would make it an attractive location, but to ensure continuity of fuel supply, it would seem most likely that they encouraged re-growth through a coppice-style system.

[38] The buildings within the St John's Wood compartment, now Leedsgate Farm, included the theatre, gym and chapel for the airbase.