Black Park Walks for All - "Miles of trails through conifer woods, around the lake or through heathland. Walks likely to be suitable for people with impaired mobility and users of wheelchairs, mobility scooters and pushchairs." - "Wheelchair accessible trails, parking, toilets and cafe. Mobility scooters available" - from the Chilterns Conservation Board  website 
- download the All Access Trail Map

also see the Buckinghamshire Country Parks website