A plan is being drawn up to introduce car parking charges at the popular Ashridge Estate.
National Trust general manager at Ashridge Estate Susie Mercer said: “We have been looking at parking charges for quite some time, it is a key priority with the National Trust.
“We have a very extensive project looking at how we introduce this.
“At the moment it is just a plan.”
Parking charges are already in place at Dunstable Downs - also National Trust land - where it costs motorists £2.50.
The Ashridge Estate, which is made up of 5,000 acres of the Chiltern Hills, was taken on by the National Trust in 1926.
Ms Mercer added: “One of the key reasons the National Trust was formed is to encourage people to get outside to enjoy the outdoors.
“We’re proud and delighted that so many people enjoy spending time at these special places but we know we have to keep on improving facilities for our visitors and ensure we get the basics right.
“That’s why we’re investing in building new, bigger car parks at many of our sites and maintaining and improving others.
“To pay for this and to help support our wider conservation and access work we need to introduce charging for non-members at some of our sites. Many National Trust places and other outdoor visitor attractions already charge for parking. Our members will continue to park for free. Free parking is just one of our many member benefits.
“We have a responsibility to protect what we look after forever and for everyone so we need to ensure we have the funds available to do so.
“We are in the very early appraisal stage and will be consulting widely on any new car parking proposals when we’ve looked at the options.”