The last major additions, on the east side of The Heath, resulted from the break-up of Lord Mansfield's estate, first projected in 1914.
The Kenwood Preservation Council in 1922 raised money to buy 100 acres, of which 9 acres east of Millfield Lane were resold to the owners of Caen Wood Towers and Beechwood subject to a ban on building.
Ken Wood itself and the lakes south of the mansion, 32 acres, were also bought, vested in the L.C.C., and in 1925 opened by George V. Kenwood House and 75 acres around it were saved from the builders by the earl of Iveagh (d. 1927), who settled them on himself for life.
He installed art treasures and left the mansion in trust as a picture gallery, which was opened in 1928.
The grounds were left to the L.C.C., as part of The Heath.
Kenwood House was taken over by the L.C.C. in 1949. In 1925 the Paddock, 1¾ acres at North End, was bought from Lord Leverhulme's executors with subscriptions.
Further small but important additions followed the Second World War as a result of bombing, demolitions, or changes of use.
They included the sites of Fern Lodge and Heathlands north of Jack Straw's Castle in 1948 and 1951, the gardens of Pitt House, 3 acres when the Elms became a hospital, the Hill gardens of Heath Lodge, and in 1967 the tollhouse at the Spaniards.
The many changes helped to account for slight variations in the figures given for the acreage.
In 1937 The Heath, including the Extension and Golders Hill Park, was estimated by the L.C.C. at 287.5 acres, Parliament Hill at 270.5 acres, and Kenwood at 195.2 acres, a total of 753.2 acres.
In 1951 The Heath was said to be 290.5 acres and the other two areas were unchanged.
In 1971 the G.L.C.'s estimated total was 802 acres.
The appearance of The Heath continued to cause concern after the possibility of direct private exploitation had been eliminated.
One controversy was about the moorland character of the old Heath, in which it differed from most of London's open spaces and from the additions made after 1871, which were either farmland or parkland.
Another was about the threat from traffic across The Heath and from inappropriate buildings overlooking it.
Neither question was finally laid to rest.
Some landscaping was needed, if only to repair the harm done by digging, which had made much of the ground 'one collection of dangerous and unsightly pits'.
The Times, regretting the M.B.W.'s six-month delay in producing any measures of ornamentation or regulation, looked forward to a tasteful conversion into 'one of the most exquisite parks in the world'.
Philip Le Breton, however, as chairman of the parks committee, favoured the restoration of natural beauty, which also met his colleagues' desire to economize.
By 1875, with the scars of excavation largely grown over, the M.B.W. won praise for a judicious neglect which had not made The Heath 'prim or park-like'.
The success of resistance to the plans of public authorities may have owed much to the prominence of many of the heath's local defenders.
The L.C.C., warned by Octavia Hill in 1890 against attempted improvements, adopted schemes for tree planting, in 1894, and tidying up, both of which brought petitions signed by distinguished protesters.
Critics were told that the need to provide shelter for visitors must affect views from some houses but were assured that it was desired to preserve the rusticity of West Heath and that gorse cutting was pruning.
The Hampstead Heath Protection society was formed in 1897, with the aim of co-operating with the L.C.C.; further planting was prevented, although thinning was not conceded until 1918.
An action group was formed in 1978 to stir up what had become The Heath and Old Hampstead Protection society, after the G.L.C. in its turn had been accused of wanting to turn the wilder parts into a typical park.
The threat from new roads and obtrusive buildings was lessened by the acquisition of East Park in 1889, which made it possible for access roads reserved in the Act of 1871 to be left as no more than tracks.
The L.C.C. at first hoped to make wider ways, with cinders from the dismantled East Park brickfields, but retreated after protests by Octavia Hill and others.
Sandy Road, skirting West Heath and bisecting Sandy Heath from West End Lane to the Spaniards, was closed to motor traffic in 1924 and thereafter formed two bridle paths.
The main roads across the old Heath, Spaniard's and North End roads, were kept free of public transport services until 1922. A proposal to demolish the tollhouse opposite the Spaniards in 1961 was successfully resisted, partly on the grounds that it would lead to more and faster traffic.
Tall or incongruous buildings overlooking The Heath had caused alarm since William Howitt's attack on the 'Tower of Babel' bulk of the castellated hotel in the Vale of Health.
The flats called The Pryors, in East Heath Road, were similarly criticized in 1903.
Projected seven-storeyed flats at Bellmoor were limited by the L.C.C., to make them fourstoreyed, in 1929, but there was a possibility of new blocks at the Old Court House and Heath Brow, near Jack Straw's Castle, in 1938.
The L.C.C.'s London development plan of 1951 would have permitted bigger buildings around The Heath, only to be disallowed by the government, and redevelopment on the bombed site at Heath Brow was averted by its purchase for a car park.
The acquisition of such plots as the Hill gardens brought further protection.
Vigilance was still needed in 1984, however, when fears sprang mainly from plans for houses in the grounds of Witanhurst, on the Highgate side of The Heath.
In the 1960s Hampstead Heath's 'romantic abrupt scenery, a bit like the hilly parts of Shropshire', was thought to give maximum effect in the smallest area.
It continued to be praised in the 1980s for its variety and in particular for its wildness.
Its future management was uncertain, after the abolition of the G.L.C. in 1986.
Proposals for a division between Camden, Barnet, and Haringey L.B.s were unwelcome to local residents and to The Heath and Old Hampstead society, as was management by the City of London to Camden and by Camden to the government.
Other possibilities were for the London Residuary Body, temporarily in charge, to be succeeded by a joint committee from three local authorities, or by a new authority, or a local trust.
It was The City of London Corporation that eventually took over the running of Hampstead Heath.
The management of The Heath is no easy matter; there are diverse sections of the community all focusing on and requiring different criteria.
C.W. (Kit) Ikin, in his "1871/1971 Hampstead Heath Centenary ~ How The Heath was saved for the public", sums these up most admirably:
"The bird watcher wants plenty of trees and bushes, preferably fenced off; the soil enthusiast wants trees to prevent erosion; the wild flower man wants fewer trees; the law-abiding man wants trees that children cannot climb; the law-and-order man wants no bushes or hedges behind which villains can skulk; some planners want large open spaces broken up into small secluded spaces; one forestry man wants a great variety of species, another to limit The Heath to native trees; those with memories or folk memoriers bewail the lost views, the disappearing gorse and bracken and the long lost heather.
What is right is probably an amalgam of these views. What is certain is that whenever the GLC fells a tree someone will complain!
My own personal regret is that the Sandy Heath, West Heath and Upper East Heath are no longer moorland, as they were from 1680 to 1890, for woodland can easily be found around London and moorland cannot.
I regret too that country meadows, hedged and with rough grass, are now so rare on The Heath. Many former meadows of this type are now either scrub woodland or open park."
City of London works to address this balance.