To claim, click "GET FREEBIE", and follow the instructions as seen on their site. To send a chocolate bar, you'll need to look out for one of their Secret Santa posters in a nearby bus stop, shop, or town centre. Once you've found your nearest poster, simply scan the QR code displayed on it, and you'll have the opportunity to send a free chocolate bar to someone you care about.
But hurry, this opportunity is only available until 11.59 pm on the 24th of December. Don't worry if you don't manage to claim one this time as all unsuccessful participants during the Postal Service Period will have the opportunity to enter a random prize draw for a second giveaway too!