When the project for the building of the Hampstead Tube with a station on the west of Hampstead Heath became known, Henrietta Barnett's first thought was of the threatened "ruin of the sylvan restfulness of that portion of the most beautiful open space near London". Her immediate reaction was the organisation of the Hampstead Heath Extension Council to save 80 acres of land from the "rows of ugly villas such as disfigure Willesden and most of the suburbs of London". The idea of the Garden Suburb grew out of the Heath Extension, for which the money was raised and the land handed over to the London County Council to be dedicated to the public as an open space forever.

The plans were outlined by Henrietta Barnett in an article in the Contemporary Review of 1905. The intention of the company, which she formed in March, 1906 with the help of influential friends, was not to be an ordinary land-owning company but to make a social experiment by providing for people of all classes a beautiful and healthy place to live in.

The broad lines of the scheme were -

• that persons of all classes of society and standards of income should be accommodated and that the handicapped be welcomed;
• that the cottages and houses should be limited on an average to eight to an acre;
• that the roads should be 40 feet wide, and that the fronts of the houses should be at least 50 feet apart, gardens occupying the intervening space;
• that the plot divisions should not be walls but hedges or trellis or wire fences;
• that every road should be lined with trees, making when possible, a colour scheme with the hedges;
• that the woods and public gardens should be free to all the tenants without regard to the amount of their ground rent, i.e., the best for all classes;
• that noise should be avoided, even to the prohibition of Church or Chapel or Institute bells;
• that lower ground rents should be charged in certain areas to enable weekly wage-earners to live on the Estate;
• that the houses be so planned that none should spoil each other's outlook or rob its neighbour of beauty.