The campaign, "#YayDelay" by MullenLowe Group, uses an algorithm to identify train delays at Waterloo station, as well as tweets with the hashtag to unlock the offer.
Passengers will need to keep an eye out on yaydelay.com to see if there has been enough activity to trigger a free drink. They can then download a voucher and pop to Slug & Lettuce outside Waterloo Station to claim their gin and tonic.
It launches today between 5pm and 6pm and Gordon’s plans to roll it out to other stations over the year.