Ingredients:
Fortified WHEAT Flour (with Calcium Carbonate, Iron, Niacin, Thiamin), Water, Dried Fermented WHEAT Flour, Dried Durum WHEAT Sourdough, Salt, Yeast, Emulsifier: Mono- and diacetyl tartaric acid esters of mono- and diglycerides of fatty acids; Flour Treatment Agent: Ascorbic Acid; Enzymes, Rapeseed Oil.
No, it's not sourdough starter. It's made by the Northern Dough Company, who say
"There aren’t many things that beat the smell of freshly baked bread in the oven. Which is why we were so excited to introduce our Sourdough bread dough to the family. If you know thing or two about making Sourdough from scratch, you’ll know it requires a good helping of time, and double measures of patience. So, being the generous folk that we are, we’ve done the hard bit, so you can fast-forward to the fun bit."
Calling it sourdough is a bit of a stretch.