Print out the voucher and visit a National Trust place for free, look on the website under offers for money off the cafes, they sometimes have a free coffee or a % off the bill.
Some National Trust places excluded but these are all listed
If above link does not work try http://www.nationaltrust.org.uk/servlet/file/store5/item811615/version1/Civic%20Voice%20free%20visit%20pass%202012-13.pdf
National trust home page
put Civic Voice in the search