Sorry if this has already been posted.
I have been using this for many months now. At Marston's restaurants, you can get a free drinks voucher when you sign up to their newsletter. I have tried this at two restaurants in Nottinghamshire and it works fine. I can't guarantee it will work everywhere, so go to the Marstons website, find your local pub, sign up to their newsletter, and see if you get a code.
There is no purchase necessary, just go to the till and tell them the code, they will enter it into the till. Here are some T+C's:
This voucher entitles the holder to ONE free drink from the following selection - A pint of any Cask Ale (excluding Guinness), a pint of Fosters (or alternative standard lager if not available), a 175ml glass of house wine, a bottle of J20 or a 14oz glass of Pepsi or Lemonade. The voucher code is only valid for 6 months from signing up. I have no idea when it will end, I first used it in Feb 2014 and it's still going.
Any questions? Feel free to ask :) Enjoy!