http://www.Shaw-Trust.org.uk/Horti.html
Shaw Trust is a national charity which enables disabled people to find a route to work  through gardening & horticulture projects. One of the many ways we help disabled people into employment is by running horticulture enterprise projects to develop some of the skills which help disabled people to work

http://www.thrive.org.uk
Thrive is a national horticultural charity.  It supports a network of specialist projects that run horticultural activity for training and employment, therapy and health.
 
http://www.tattongardensociety.co.uk
Tatton Garden Society is a registered Charity whose aim is to educate the public on all matters relating to gardening. Based at Tatton Park, Knutsford, a NT property.

http://www.gardeners-grbs.org.uk
The Gardeners' Royal Benevolent Society is a charitable organisation which has been helping disabled or retired gardeners and associated tradespersons for over 160 years