The organisation is in discussion with the Inland Revenue about replacing admission tickets with day passes in order to take advantage of the Gift Aid scheme.
Day passes classify as a donation rather than a purchase, qualifying them for Gift Aid, which can only be claimed on outright gifts to charity.
If day passes get the go-ahead the trust could claim back 28p on top of every £1 donated.
Under the proposed scheme, when entering a National Trust property UK citizens would be required to fill in their name and address details and sign a Gift Aid declaration to enable the trust to claim tax back.
The trust is currently looking at locations that have a high number of non-member visitors passing through and wants to encourage them to participate in the pilot.
However, the trust is worried about the effects the scheme may have on recruiting new members as it does not want to bombard visitors with too many forms. "There is a lot we ask of our visitors when they walk through the gates so we need to tread very carefully as we do not want it to cut across our current membership," said Gill Raikes, assistant director of fundraising at the trust. "Membership is core to the charity and we would not do anything to jeopardise that."
Raikes is currently working out the value of Gift Aid for each property based on the number of non-members visiting as well as estimating a total for all properties.
Following the evaluation process, trials will begin at selected locations in the spring when most trust properties open for the season.