M&S is surprising one million of its Sparks loyalty customers with a free chocolate bar as part of its latest Sparks Tuesday offer this week. How to claim free M&S chocolate bar in Sparks appTo see if you've been selected, check the M&S app for the offer. New offers are released every week for all 24 million Sparks members as part of the retailer’s ongoing loyalty programme. An M&S Sparks spokesperson said: "What better way to make this Tuesday a little sweeter than with free chocolate? Are you hoping to get a free chocolate bar?