There is a fundamental difference in quality, both in architecture and in landscaping between the earlier part of the Garden Suburb and the later part which was laid out after 1918 under the direction of J C S Soutar. This is only partly due to the superiority of Unwin's ability over Soutar's. It is due far more to the decision by the Old Hampstead Garden Suburb Trust and the co-partnership companies to relinquish the most important social and physical ideals which had guided the Garden Suburb's planners before the War, largely as a result of the inflation of building costs in 1919-20. Apart from the completion of areas laid out earlier, the development of the Garden Suburb after 1918 consisted almost entirely of conventional houses for sale. There was no attempt to create a socially balanced community, even though that had been achieved to a remarkable extent in the earlier part. This renunciation of social idealism was paralleled by a surrender of the architectural and landscaping values.
The Old Trust took additional land at Turner's Wood and Winnington Road on lease from the Church Commissioners in 1930. Co-partnership Tenants absorbed Hampstead Heath Extension Tenants and Oakwood Tenants in 1930, and absorbed Hampstead Tenants and Second Hampstead Tenants in 1935. On both these amalgamations dividends on rents disappeared. The houses were being built for sale and not for letting. In 1939 Co-partnership Tenants was converted into a company under the Companies Act, and in 1954 it failed in a bid to acquire a majority holding in the Old Trust. The bid was made since the leases held from the Trust were perpetually renewable with rent revisions every 99 years and it was likely that in 2006 they would have to face a change from the old subsidised ground rents to economic ground rents. In 1957 Co-partnership Tenants changed its name to Suburb Leaseholds Limited.
The Church Commissioners sold their respective freeholds to the Old Trust and to Suburb Leaseholds in 1959. In the same year the five directors of Suburb Leaseholds accepted an offer from Metrovincial Properties who were later taken over by City Centre Properties. Suburb Leaseholds became a subsidiary with the principal objects of a property investment company. In 1961 the Old Trust contracted to grant a 2, 000 year lease on most of the land in their ownership to Suburb Leaseholds Limited, subject to a number of covenants. As a result of granting the 2, 000 year lease, the Old Trust was left in possession of a substantial capital sum which exceeded the maximum entitlement of its shareholders in any liquidation. It was decided that the Old Trust should be placed in liquidation in order to release the surplus funds for the benefit of the Garden Suburb.