The Gardens Trust

The only national charity dedicated to the research and conservation of designed landscapes in England and Wales and to campaign on their behalf. As the statutory consultee for Registered Parks and Gardens, they play a key conservation role and support the County Gardens Trusts in protecting and conserving our landscape heritage.

There are lots of useful information and guidance notes to be found on their website. 

thegardenstrust.org

oxfordshire
warwickshire
hereford & worcs
wiltshire
avon