Another MyFitnessPal user here. It's a great application and the database of UK foods is excellent.
Sometimes though you'll scan the barcode on a own-brand product and find that it comes up with the right product but from the wrong supermarket. For example I recently scanned M&S West Country cheddar and the database brought up Morrisons Davidstow cheddar. I guess they're both made by the same manufacturer so it doesn't make too much difference in the end.