Filled up with diesel in Tesco Cardiff five days ago - brand new Audi on second fill. Within 70 miles it broke down under frightening circumstances on motorway. No warning lights and AA/Audi could not diagnose a fault. Did call Tescos who were supposed to call me back, instead they have written today and denied any responsibility "as no one else has complained" and "Over time sediment can build up in the tanks". Main dealer believed it to be fuel related, stating fuel smelt slightly different, not as strong as diesel normally does etc. They drained and replaced fuel filter and the car runs fine again. I cannot believe Tesco dismissed our complaint out of hand without ringing me to discuss or even waiting for a garage report. Any advice appreciated or am I flogging a dead horse. Have asked garage to put their findings in writing. I only want the cash for my wasted fuel and my company wants its garage costs back.