dodgy poor quality fuel

Filled up at Morrisons (Hillsborough, Sheffield) on 22/08/2014 with unleaded only cause I had been given a 6 pence a litle voucher off my fuel by my dad, I normally use shell as the customer service is much better don't expect customers to stand and wait while one is serving and two are gassing in the back.
Within a few miles of there garage though my fiesta losing power and kanagrooing. Had my car back in with my regular mechanic who was baffled as to what problem was and had plugs off to make sure not a a bad connection or any grease on them.
In the end he contacted Ford who said it was highly unlikly the plugs due to age of car and milage but they agreed to him changing them under warrenty. Still problem persisted not as bad but it was still there. In the end my mechanic advised going to a main Ford dealer to see if they could shed some light on issue. When I went into dealer to book car in service guy said by any chance have you filled up at Morrisons I said yes they have been getting alot of cars in with same problem more so on diesels all after filling up at Morrisons. Service guy told me Morrisons buying dirty/poor fuel. They had car in to check over for any damage to anything on car but nothing told me to fill car up with good quality fuel from big company such as Shell. My regualr mechanic had heard of it happening with diesel cars but not with petrol
I have contacted Morrisons over matter as it has cost me to have in dealer, the inconvience of having it back and forth in to my mechanic and Morrisons response was no one else has complained and that that they can assure me they only sell quality fuel well Morrisons I have news for you you don't.
Disgracful attitude from Morrisons they haven't checked that anyone else has complained as there response back to me was too quick.
Will never set foot in Morrisons again and if I could give them a minus 70 score on here I would