The right of admission is disregarded as being a benefit for the purposes of the Gift Aid rules providing certain conditions are fulfilled, in particular:
Gift Aid can apply to a ‘family ticket’ donation providing a qualifying right of admission is given to the donor and their family. The right of admission does not have to be used by all of the family members at the same time.
A donation will not qualify for Gift Aid if the terms and conditions of an admission fee allow for a full or partial repayment, for example in case of bad weather.
The right of admission must be granted by the charity for the purpose of viewing property preserved, maintained kept or created by a charity (not necessarily the charity charging the admission fee) in pursuit of its charitable purposes.
HMRC has published full guidance on the matter of Gift Aid on donations that attract a right of free admission to charity property.