Here are some links to conservation and similar organisations that may be of interest:
BBOWT (Berks Bucks and Oxon Wildlife Trust) http://www.bbowt.org.uk
Woodland Trust http://www.woodlandtrust.org.uk
Plantlife http://www.plantlife.org.uk
North Wessex Downs Area of Outstanding Natural Beauty http://www.northwessexdowns.org.uk
National Trust https://www.nationaltrust.org.uk
Natural England
https://www.gov.uk/government/organisations/natural-england
The River Lambourn Renewal Project http://www.renewalproject.org.uk