Extensive quarrying has impacted much of the monument's setting to the north and west of the henges. The site lies within the wider
Nosterfield quarry area being exploited for gravel by
Tarmac Northern Ltd. In the early 21st century Tarmac planned to extend its quarrying operations to a site less than a mile east of the henges known as 'Ladybridge Farm'. Preliminary investigations of this area of land to discern its archaeological significance suggested that it may have been a location of ritual Neolithic encampments, possibly used by those people who built or visited the henges. Opponents of the plan claimed that if permission was granted for this area to be quarried, much of the remaining contextual information about the henges would be lost. A campaign led by local people and concerned archaeologists attempted to persuade Tarmac and
North Yorkshire County Council to guarantee the protection of the area.
British planning and archaeology guidelines prefer preservation
in situ of archaeological remains. In cases where this is not possible, such as quarrying, preservation by record is an option, involving archaeological
excavation. Campaigners argued that further excavation and subsequent quarrying will destroy the ritual landscape completely. In 2002, Tarmac Northern Ltd. expressed an intention to apply for planning permission to quarry Thornborough Moor, thus intending to quarry right up to the edge of the designated scheduled monument area, which caused what The Times labelled as "unprecedented protests", and a 10,000 signature petition against the proposal. In March 2005, Tarmac stated it would not seek to apply for planning permission to quarry this site for at least ten years, the period covered by North Yorkshire County Council's Minerals Plan. In February 2006, North Yorkshire County Council turned down Tarmac's application to expand quarrying to the Ladybridge Farm site. Later in 2006 Tarmac submitted a revised planning application to North Yorkshire County Council. The revised application for Ladybridge, which is adjacent to the Nosterfield Quarry, reduced the proposed area for sand and gravel extraction from 45 hectares to 31 hectares, avoiding the south west section of the site to address concerns raised about archaeology. The application was approved in February 2007. Late in 2007 campaign group Friends of Thornborough requested a judicial review of the planning permission due to a number of procedural irregularities. In response, North Yorkshire County Council ruled the permission to be "fatally flawed," and withdrew the permission previously granted. In November 2016, North Yorkshire County Council’s planning committee agreed with the owners Tarmac to approve further quarrying in return for preserving the site of the Thornborough Henges and 90 acres of surrounding land, which would eventually be handed over to a public body. This agreement saw control of the two henges on land owned by Tarmac pass to
Historic England in February 2023. The site is operated by
English Heritage and will enable public access. It will join the National Heritage Collection of
English Heritage properties. In February 2024 English Heritage announced that it had acquired the third henge from its private owners. ==References==