Uses of the words ‘public space’ and ‘open space’ over time:
Ngram of word usage in Hansard House of Commons parliamentary debates, from Hansard at Huddersfield: https://hansard.hud.ac.uk/site/site.php

Google Books Ngram viewer, open space and public space word frequency in their digitised books collection:
Open space standard targets:
date | acres per 1000 people | Target increase of open space | |
National Playing Fields Association | 1925 | 7 (4 of public land; 3 of private playing fields) | |
Open Space Standard Report | 1938 | 6 | |
County of London Plan (Abercrombie) | 1943 | 7 (4 within County; 3 within Green Belt) | 5400 acres |
L.C.C. | 1945 | 2.5 interim target | 1450 acres (1951 development plan) |
Ministry of Housing & Local Government | 1956 | 6 |
Town Planning Review, 63: 4 (1992)
Legislation relating to commons (also go to the timeline page):
Notes from Survey of Commons report, 24 March 1943 (TNA, MAF 48/351, Commons Village Greens and Recreation Grounds post-war policy documents):
Inclosure Act 1845 – rarely used, last case finished in 1918
Metropolitan Commons Act 1866 – last case 1935
Commons Act 1876 – necessity for enclosure rather than regulation must be proved – rarely used because of expense and complicated procedure – last case 1936
Commons Act 1899 – approval of schemes made by local authorities for control and improvement – frequent cases in ‘normal times’
Commons Act 1893 – lords of the manor consent – cases infrequent
Commons Act 1906 – approval of regulation schemes
Law of Property Act 1925 – sec.193 – right of access for air and exercise to all urban commons
1990
legal definition in the Town and Country Planning Act of 1990 (https://www.legislation.gov.uk/ukpga/1990/8/section/336)
“open space” means any land laid out as a public garden, or used for the purposes of public recreation, or land which is a disused burial ground’
and the more traditional planning definition of Public Open Space.
It also notes the additional category of ‘public green space’, including urban parks and gardens, country parks and canal and riverbanks.
2004
2004 government report, Living Places: Caring for Quality, https://www.futurecommunities.net/files/images/ving_Places_Caring_for_Quality_Report__ODPM_.pdf, which defines ‘public realm’ as
‘all those parts of the built environment where the public has free access. It encompasses: all streets, squares and other rights of way, whether predominantly in residential, commercial or community/civic uses; the open spaces and parks; and the ‘public/private’ spaces where public access is unrestricted (at least during daylight hours). It includes the interfaces with key internal and private spaces to which the public normally has free access’.
2011
Definition from the London Assembly’s 2011’s report, ‘Public life in private hands Managing London’s public space’, which started to acknowledge the massive shift to privately-owned public spaces in the capital.

‘all spaces including streets, squares and parks that everyone can use and access in principle, regardless of who owns or manages the space’.
2014
Government guidance 2014 for open space considerations in planning:
See also the 2014 government guidance about the definitions of Open Green Space in relation to planning and sport: https://www.gov.uk/guidance/open-space-sports-and-recreation-facilities-public-rights-of-way-and-local-green-space



Common rights and the right of recreation:
‘The Right of Recreation’ by Humphrey Baker, in the annual report of the Commons and Footpath Preservation Society, vol V, 1937, pp. 176-77:





