See here for details.
And of every one of these threads someone comes on and says, "But why shouldn't I get clubcard points on formula?" or, "I don't know anyone who would stop bf-ing because they might get clubcard points." The point is, it's against Code for a reason. Formula milk should not be something which has extra incentives added to it, anymore than Nestle should sponsor nurses in the Phillipines, or Bounty hand out mini pots of Sudocrem.
Please do complain to Tesco and to Trading Standards. It's insane that Tesco have done this, when they must know full well what the marketing code for infant formula is.