Found via MSE.
1. Go into Tesco store (excludes Tesco Express) and find the Casillero del Diablo Merlot Chile 75cl wine (no other wine works on the brand match) You must buy at least six bottles to get the 25% off (but you could buy a max of eight) to make the most of this glitch as you’ll only get a maximum of £20 back in the Brand Guarantee.
2. Add in nine different items to automatically trigger the Brand Guarantee, which comes into effect if you’re buying at least 10 different items (the wine counts as one). Try to find some cheap items, such as a banana or carrot – or ideally things you’d normally buy anyway. See our Tesco Brand Guarantee news story for how it works.
3. Take your items to the checkout (we used the self-service till). If it’s worked, you’ll see your total go down by around half when you go to checkout.
Some cheap items I found that you can add into your shop (to get you to the 10 items) include individual carrots for 6p, Haribo sweets for 10p and a single banana for 12p.
Casillero del Diablo Reserva Chardonnay Chile Will also work.