In 1891, the Salvation Army bought the Castle, along with 800 acres of farmland at Hadleigh, incorporating three farms to the south of the village - Castle, Park and Sayers Farms. The land was to be used as a colony to rescue the poor and destitute from the squalor of London, train them in agriculture and general farming practices and then find them jobs in Britain or abroad. By 1892, 11 new buildings had been built. A diary and poultry farms, piggeries, granary, mill, and the first of the brickfields were established. A tramway and railway were built, linking to a wharf on Hadleigh Ray. The remains of this can still be seen. By 1898, there were 300 acres of arable fields, orchards, an 80 acre market garden, beehives and a rabbit warren. The brickfields, served by 3.5 miles of railway, produced 50,000 bricks a day in the summer months. These bricks can still be found around the area and may be recognised by their yellow colour. The colony was a tourist attraction and had an unofficial hotel and refreshment facilities. By 1905, the total population of the colony was 500.

During the colony’s heyday (1891 - 1914), an average of 400 people passed through each year. Initially, men were only going to stay for 6 months, but experience showed that longer stays were necessary. New probationers were started on basic tasks at Leigh Park Farm. As their health improved, they were transferred to the main colony for more complex work. As a probationer progressed, the standard of accommodation and the size of the food grant (paid in the colony’s own coinage) improved. All colonists were required to attend Sunday meetings in the Citadel, and were not allowed to drink alcohol, smoke or swear. After the completion of rehabilitation, colonists were encouraged to return to their families, or go abroad. Thousands chose to emigrate, via the SA Emigration Dept., whilst some settled locally, and some local families can trace their ancestry back to a colonist. After WW1, when all able-bodied men were called up, the Colony became a training camp for boys aged 14 - 19.

In 1923, the ruins were in decay and in parts dangerous, due to demolition by the S. A. for use in road building, although some money had been spent by them on repairs prior to World War 1.

In 1936, Essex County Council recommended preservation of the castle and 354 acres, but World War 2 prevented this.

During WW2, land around the castle was used for an anti-aircraft battery, a troop camp, a searchlight position and pigeon breeding lofts. Many of these concrete buildings can still be seen. Paid hands and Land Army girls worked the land. The brickworks worked at a fraction of their capacity.

In 1948, the ruins of the castle were handed over to the Ministry of Works and repairs started.

During the 1950s, the colony continued to decline as agriculture became more mechanised. The colony officially closed in 1968, and the farm is now managed on a commercial basis. Many of the buildings were demolished, and the brickfields were either landfilled or flooded.

Between 1969 and 1970, major landslips threatened the towers with collapse.

In 1971 the Department of the Environment undertook excavation and conservation work.

Hadleigh Country Park